* mh-e: Created directory. ChangeLog will appear in a week when we

release version 7.2.

* lisp/mail/mh-alias.el, lisp/mail/mh-comp.el,
lisp/mail/mh-customize.el, lisp/mail/mh-e.el, lisp/mail/mh-funcs.el,
lisp/mail/mh-identity.el, lisp/mail/mh-index.el,
lisp/mail/mh-loaddefs.el, lisp/mail/mh-mime.el, lisp/mail/mh-pick.el,
lisp/mail/mh-seq.el, lisp/mail/mh-speed.el, lisp/mail/mh-utils.el,
lisp/mail/mh-xemacs-compat.el: Moved to mh-e. Note that reply2.pbm and
reply2.xpm, which were created by the MH-E package, were left in mail
since they can probably be used by other mail packages.

* makefile.w32-in (WINS): Added mh-e.

* makefile.nt (WINS): Added mh-e.

1 files changed, 1277 insertions, 0 deletions

diff --git a/lisp/mh-e/mh-seq.el b/lisp/mh-e/mh-seq.el
new file mode 100644
index 00000000000..d3859821ae1
--- /dev/null
+++ b/lisp/mh-e/mh-seq.el
@@ -0,0 +1,1277 @@
+;;; mh-seq.el --- MH-E sequences support
+
+;; Copyright (C) 1993, 1995, 2001, 2002 Free Software Foundation, Inc.
+
+;; Author: Bill Wohler <wohler@newt.com>
+;; Maintainer: Bill Wohler <wohler@newt.com>
+;; Keywords: mail
+;; See: mh-e.el
+
+;; This file is part of GNU Emacs.
+
+;; GNU Emacs is free software; you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation; either version 2, or (at your option)
+;; any later version.
+
+;; GNU Emacs is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with GNU Emacs; see the file COPYING.  If not, write to the
+;; Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+;; Boston, MA 02111-1307, USA.
+
+;;; Commentary:
+;;
+;;   This tries to implement the algorithm described at:
+;;     http://www.jwz.org/doc/threading.html
+;;   It is also a start to implementing the IMAP Threading extension RFC. The
+;;   implementation lacks the reference and subject canonicalization of the
+;;   RFC.
+;;
+;;   In the presentation buffer, children messages are shown indented with
+;;   either [ ] or < > around them. Square brackets ([ ]) denote that the
+;;   algorithm can point out some headers which when taken together implies
+;;   that the unindented message is an ancestor of the indented message. If
+;;   no such proof exists then angles (< >) are used.
+;;
+;;   Some issues and problems are as follows:
+;;
+;;    (1) Scan truncates the fields at length 512. So longer references:
+;;        headers get mutilated. The same kind of MH format string works when
+;;        composing messages. Is there a way to avoid this? My scan command
+;;        is as follows:
+;;          scan +folder -width 10000 \
+;;               -format "%(msg)\n%{message-id}\n%{references}\n%{subject}\n"
+;;        I would really appreciate it if someone would help me with this.
+;;
+;;    (2) Implement heuristics to recognize message-id's in In-Reply-To:
+;;        header. Right now it just assumes that the last text between angles
+;;        (< and >) is the message-id. There is the chance that this will
+;;        incorrectly use an email address like a message-id.
+;;
+;;    (3) Error checking of found message-id's should be done.
+;;
+;;    (4) Since this breaks the assumption that message indices increase as
+;;        one goes down the buffer, the binary search based mh-goto-msg
+;;        doesn't work. I have a simpler replacement which may be less
+;;        efficient.
+;;
+;;    (5) Better canonicalizing for message-id and subject strings.
+;;
+
+;; Internal support for MH-E package.
+
+;;; Change Log:
+
+;; $Id: mh-seq.el,v 1.10 2003/01/08 23:21:16 wohler Exp $
+
+;;; Code:
+
+(require 'cl)
+(require 'mh-e)
+
+;; Shush the byte-compiler
+(defvar tool-bar-mode)
+
+;;; Data structures (used in message threading)...
+(defstruct (mh-thread-message (:conc-name mh-message-)
+                              (:constructor mh-thread-make-message))
+  (id nil)
+  (references ())
+  (subject "")
+  (subject-re-p nil))
+
+(defstruct (mh-thread-container (:conc-name mh-container-)
+                                (:constructor mh-thread-make-container))
+  message parent children
+  (real-child-p t))
+
+
+;;; Internal variables:
+(defvar mh-last-seq-used nil
+  "Name of seq to which a msg was last added.")
+
+(defvar mh-non-seq-mode-line-annotation nil
+  "Saved value of `mh-mode-line-annotation' when narrowed to a seq.")
+
+;;; Maps and hashes...
+(defvar mh-thread-id-hash nil
+  "Hashtable used to canonicalize message-id strings.")
+(defvar mh-thread-subject-hash nil
+  "Hashtable used to canonicalize subject strings.")
+(defvar mh-thread-id-table nil
+  "Thread ID table maps from message-id's to message containers.")
+(defvar mh-thread-id-index-map nil
+  "Table to lookup message index number from message-id.")
+(defvar mh-thread-index-id-map nil
+  "Table to lookup message-id from message index.")
+(defvar mh-thread-scan-line-map nil
+  "Map of message index to various parts of the scan line.")
+(defvar mh-thread-old-scan-line-map nil
+  "Old map of message index to various parts of the scan line.
+This is the original map that is stored when the folder is narrowed.")
+(defvar mh-thread-subject-container-hash nil
+  "Hashtable used to group messages by subject.")
+(defvar mh-thread-duplicates nil
+  "Hashtable used to remember multiple messages with the same message-id.")
+(defvar mh-thread-history ()
+  "Variable to remember the transformations to the thread tree.
+When new messages are added, these transformations are rewound, then the
+links are added from the newly seen messages. Finally the transformations are
+redone to get the new thread tree. This makes incremental threading easier.")
+(defvar mh-thread-body-width nil
+  "Width of scan substring that contains subject and body of message.")
+
+(make-variable-buffer-local 'mh-thread-id-hash)
+(make-variable-buffer-local 'mh-thread-subject-hash)
+(make-variable-buffer-local 'mh-thread-id-table)
+(make-variable-buffer-local 'mh-thread-id-index-map)
+(make-variable-buffer-local 'mh-thread-index-id-map)
+(make-variable-buffer-local 'mh-thread-scan-line-map)
+(make-variable-buffer-local 'mh-thread-old-scan-line-map)
+(make-variable-buffer-local 'mh-thread-subject-container-hash)
+(make-variable-buffer-local 'mh-thread-duplicates)
+(make-variable-buffer-local 'mh-thread-history)
+
+;;;###mh-autoload
+(defun mh-delete-seq (sequence)
+  "Delete the SEQUENCE."
+  (interactive (list (mh-read-seq-default "Delete" t)))
+  (mh-map-to-seq-msgs 'mh-notate-if-in-one-seq sequence ?  (1+ mh-cmd-note)
+                      sequence)
+  (mh-undefine-sequence sequence '("all"))
+  (mh-delete-seq-locally sequence))
+
+;; Avoid compiler warnings
+(defvar view-exit-action)
+
+;;;###mh-autoload
+(defun mh-list-sequences ()
+  "List the sequences defined in the folder being visited."
+  (interactive)
+  (let ((folder mh-current-folder)
+        (temp-buffer mh-temp-sequences-buffer)
+        (seq-list mh-seq-list)
+        (max-len 0))
+    (with-output-to-temp-buffer temp-buffer
+      (save-excursion
+        (set-buffer temp-buffer)
+        (erase-buffer)
+        (message "Listing sequences ...")
+        (insert "Sequences in folder " folder ":\n")
+        (let ((seq-list seq-list))
+          (while seq-list
+            (setq max-len
+                  (max (length (symbol-name (mh-seq-name (pop seq-list))))
+                       max-len)))
+          (setq max-len (+ 2 max-len)))
+        (while seq-list
+          (let ((name (mh-seq-name (car seq-list)))
+                (sorted-seq-msgs
+                 (mh-coalesce-msg-list
+                  (sort (copy-sequence (mh-seq-msgs (car seq-list))) '<)))
+                name-spec)
+            (insert (setq name-spec (format (format "%%%ss:" max-len) name)))
+            (while sorted-seq-msgs
+              (let ((next-element (format " %s" (pop sorted-seq-msgs))))
+                (when (>= (+ (current-column) (length next-element))
+                          (window-width))
+                  (insert "\n")
+                  (insert (format (format "%%%ss" (length name-spec)) "")))
+                (insert next-element)))
+            (insert "\n"))
+          (setq seq-list (cdr seq-list)))
+        (goto-char (point-min))
+        (view-mode 1)
+        (setq view-exit-action 'kill-buffer)
+        (message "Listing sequences...done")))))
+
+;;;###mh-autoload
+(defun mh-msg-is-in-seq (message)
+  "Display the sequences that contain MESSAGE (default: current message)."
+  (interactive (list (mh-get-msg-num t)))
+  (let* ((dest-folder (loop for seq in mh-refile-list
+                            when (member message (cdr seq)) return (car seq)))
+         (deleted-flag (unless dest-folder (member message mh-delete-list))))
+    (message "Message %d%s is in sequences: %s"
+             message
+             (cond (dest-folder (format " (to be refiled to %s)" dest-folder))
+                   (deleted-flag (format " (to be deleted)"))
+                   (t ""))
+             (mapconcat 'concat
+                        (mh-list-to-string (mh-seq-containing-msg message t))
+                        " "))))
+
+;;;###mh-autoload
+(defun mh-narrow-to-seq (sequence)
+  "Restrict display of this folder to just messages in SEQUENCE.
+Use \\<mh-folder-mode-map>\\[mh-widen] to undo this command."
+  (interactive (list (mh-read-seq "Narrow to" t)))
+  (with-mh-folder-updating (t)
+    (cond ((mh-seq-to-msgs sequence)
+           (mh-widen)
+           (mh-remove-all-notation)
+           (let ((eob (point-max))
+                 (msg-at-cursor (mh-get-msg-num nil)))
+             (setq mh-thread-old-scan-line-map mh-thread-scan-line-map)
+             (setq mh-thread-scan-line-map (make-hash-table :test #'eql))
+             (mh-copy-seq-to-eob sequence)
+             (narrow-to-region eob (point-max))
+             (mh-notate-user-sequences)
+             (mh-notate-deleted-and-refiled)
+             (mh-notate-seq 'cur mh-note-cur mh-cmd-note)
+             (when msg-at-cursor (mh-goto-msg msg-at-cursor t t))
+             (make-variable-buffer-local 'mh-non-seq-mode-line-annotation)
+             (setq mh-non-seq-mode-line-annotation mh-mode-line-annotation)
+             (setq mh-mode-line-annotation (symbol-name sequence))
+             (mh-make-folder-mode-line)
+             (mh-recenter nil)
+             (if (and (boundp 'tool-bar-mode) tool-bar-mode)
+                 (set (make-local-variable 'tool-bar-map)
+                      mh-folder-seq-tool-bar-map))
+             (setq mh-narrowed-to-seq sequence)
+             (push 'widen mh-view-ops)))
+          (t
+           (error "No messages in sequence `%s'" (symbol-name sequence))))))
+
+;;;###mh-autoload
+(defun mh-put-msg-in-seq (msg-or-seq sequence)
+  "Add MSG-OR-SEQ (default: displayed message) to SEQUENCE.
+If optional prefix argument provided, then prompt for the message sequence.
+If variable `transient-mark-mode' is non-nil and the mark is active, then
+the selected region is added to the sequence."
+  (interactive (list (cond
+                      ((mh-mark-active-p t)
+                       (mh-region-to-msg-list (region-beginning) (region-end)))
+                      (current-prefix-arg
+                       (mh-read-seq-default "Add messages from" t))
+                      (t
+                       (mh-get-msg-num t)))
+                     (mh-read-seq-default "Add to" nil)))
+  (if (not (mh-internal-seq sequence))
+      (setq mh-last-seq-used sequence))
+  (mh-add-msgs-to-seq (cond ((numberp msg-or-seq) (list msg-or-seq))
+                            ((listp msg-or-seq) msg-or-seq)
+                            (t (mh-seq-to-msgs msg-or-seq)))
+                      sequence))
+
+(defun mh-valid-view-change-operation-p (op)
+  "Check if the view change operation can be performed.
+OP is one of 'widen and 'unthread."
+  (cond ((eq (car mh-view-ops) op)
+         (pop mh-view-ops))
+        (t nil)))
+
+;;;###mh-autoload
+(defun mh-widen ()
+  "Remove restrictions from current folder, thereby showing all messages."
+  (interactive)
+  (let ((msg (mh-get-msg-num nil)))
+    (when mh-narrowed-to-seq
+      (cond ((mh-valid-view-change-operation-p 'widen) nil)
+            ((memq 'widen mh-view-ops)
+             (while (not (eq (car mh-view-ops) 'widen))
+               (setq mh-view-ops (cdr mh-view-ops)))
+             (pop mh-view-ops))
+            (t (error "Widening is not applicable")))
+      (when (memq 'unthread mh-view-ops)
+        (setq mh-thread-scan-line-map mh-thread-old-scan-line-map))
+      (with-mh-folder-updating (t)
+        (delete-region (point-min) (point-max))
+        (widen)
+        (setq mh-mode-line-annotation mh-non-seq-mode-line-annotation)
+        (mh-make-folder-mode-line))
+      (if msg
+          (mh-goto-msg msg t t))
+      (mh-notate-deleted-and-refiled)
+      (mh-notate-user-sequences)
+      (mh-notate-seq 'cur mh-note-cur mh-cmd-note)
+      (mh-recenter nil)))
+  (if (and (boundp 'tool-bar-mode) tool-bar-mode)
+      (set (make-local-variable 'tool-bar-map) mh-folder-tool-bar-map))
+  (setq mh-narrowed-to-seq nil))
+
+;; FIXME?  We may want to clear all notations and add one for current-message
+;;         and process user sequences.
+(defun mh-notate-deleted-and-refiled ()
+  "Notate messages marked for deletion or refiling.
+Messages to be deleted are given by `mh-delete-list' while messages to be
+refiled are present in `mh-refile-list'."
+  (mh-mapc #'(lambda (msg) (mh-notate msg mh-note-deleted mh-cmd-note))
+           mh-delete-list)
+  (mh-mapc #'(lambda (dest-msg-list)
+               ;; foreach folder name, get the keyed sequence from mh-seq-list
+               (let ((msg-list (cdr dest-msg-list)))
+                 (mh-mapc #'(lambda (msg)
+                              (mh-notate msg mh-note-refiled mh-cmd-note))
+                          msg-list)))
+           mh-refile-list))
+
+
+
+;;; Commands to manipulate sequences.  Sequences are stored in an alist
+;;; of the form:
+;;;     ((seq-name msgs ...) (seq-name msgs ...) ...)
+
+(defun mh-read-seq-default (prompt not-empty)
+  "Read and return sequence name with default narrowed or previous sequence.
+PROMPT is the prompt to use when reading. If NOT-EMPTY is non-nil then a
+non-empty sequence is read."
+  (mh-read-seq prompt not-empty
+               (or mh-narrowed-to-seq
+                   mh-last-seq-used
+                   (car (mh-seq-containing-msg (mh-get-msg-num nil) nil)))))
+
+(defun mh-read-seq (prompt not-empty &optional default)
+  "Read and return a sequence name.
+Prompt with PROMPT, raise an error if the sequence is empty and the NOT-EMPTY
+flag is non-nil, and supply an optional DEFAULT sequence. A reply of '%'
+defaults to the first sequence containing the current message."
+  (let* ((input (completing-read (format "%s %s %s" prompt "sequence:"
+                                         (if default
+                                             (format "[%s] " default)
+                                           ""))
+                                 (mh-seq-names mh-seq-list)))
+         (seq (cond ((equal input "%")
+                     (car (mh-seq-containing-msg (mh-get-msg-num t) nil)))
+                    ((equal input "") default)
+                    (t (intern input))))
+         (msgs (mh-seq-to-msgs seq)))
+    (if (and (null msgs) not-empty)
+        (error "No messages in sequence `%s'" seq))
+    seq))
+
+(defun mh-seq-names (seq-list)
+  "Return an alist containing the names of the SEQ-LIST."
+  (mapcar (lambda (entry) (list (symbol-name (mh-seq-name entry))))
+          seq-list))
+
+;;;###mh-autoload
+(defun mh-rename-seq (sequence new-name)
+  "Rename SEQUENCE to have NEW-NAME."
+  (interactive (list (mh-read-seq "Old" t)
+                     (intern (read-string "New sequence name: "))))
+  (let ((old-seq (mh-find-seq sequence)))
+    (or old-seq
+        (error "Sequence %s does not exist" sequence))
+    ;; create new sequence first, since it might raise an error.
+    (mh-define-sequence new-name (mh-seq-msgs old-seq))
+    (mh-undefine-sequence sequence (mh-seq-msgs old-seq))
+    (rplaca old-seq new-name)))
+
+;;;###mh-autoload
+(defun mh-map-to-seq-msgs (func seq &rest args)
+  "Invoke the FUNC at each message in the SEQ.
+SEQ can either be a list of messages or a MH sequence. The remaining ARGS are
+passed as arguments to FUNC."
+  (save-excursion
+    (let ((msgs (if (listp seq) seq (mh-seq-to-msgs seq))))
+      (while msgs
+        (if (mh-goto-msg (car msgs) t t)
+            (apply func (car msgs) args))
+        (setq msgs (cdr msgs))))))
+
+;;;###mh-autoload
+(defun mh-notate-seq (seq notation offset)
+  "Mark the scan listing.
+All messages in SEQ are marked with NOTATION at OFFSET from the beginning of
+the line."
+  (mh-map-to-seq-msgs 'mh-notate seq notation offset))
+
+;;;###mh-autoload
+(defun mh-add-to-sequence (seq msgs)
+  "The sequence SEQ is augmented with the messages in MSGS."
+  ;; Add to a SEQUENCE each message the list of MSGS.
+  (if (not (mh-folder-name-p seq))
+      (if msgs
+          (apply 'mh-exec-cmd "mark" mh-current-folder "-add"
+                 "-sequence" (symbol-name seq)
+                 (mh-coalesce-msg-list msgs)))))
+
+;; This has a tricky bug. mh-map-to-seq-msgs uses mh-goto-msg, which assumes
+;; that the folder buffer is sorted. However in this case that assumption
+;; doesn't hold. So we will do this the dumb way.
+;(defun mh-copy-seq-to-point (seq location)
+;  ;; Copy the scan listing of the messages in SEQUENCE to after the point
+;  ;; LOCATION in the current buffer.
+;  (mh-map-to-seq-msgs 'mh-copy-line-to-point seq location))
+
+(defun mh-copy-seq-to-eob (seq)
+  "Copy SEQ to the end of the buffer."
+  ;; It is quite involved to write something which will work at any place in
+  ;; the buffer, so we will write something which works only at the end of
+  ;; the buffer. If we ever need to insert sequences in the middle of the
+  ;; buffer, this will need to be fixed.
+  (save-excursion
+    (let* ((msgs (mh-seq-to-msgs seq))
+           (coalesced-msgs (mh-coalesce-msg-list msgs)))
+      (goto-char (point-max))
+      (save-restriction
+        (narrow-to-region (point) (point))
+        (mh-regenerate-headers coalesced-msgs t)
+        (cond ((memq 'unthread mh-view-ops)
+               ;; Populate restricted scan-line map
+               (goto-char (point-min))
+               (while (not (eobp))
+                 (let ((msg (mh-get-msg-num nil)))
+                   (when (numberp msg)
+                     (setf (gethash msg mh-thread-scan-line-map)
+                           (mh-thread-parse-scan-line))))
+                 (forward-line))
+               ;; Remove scan lines and read results from pre-computed tree
+               (delete-region (point-min) (point-max))
+               (let ((thread-tree (mh-thread-generate mh-current-folder ()))
+                     (mh-thread-body-width
+                      (- (window-width) mh-cmd-note
+                         (1- mh-scan-field-subject-start-offset)))
+                     (mh-thread-last-ancestor nil))
+                 (mh-thread-generate-scan-lines thread-tree -2)))
+              (mh-index-data
+               (mh-index-insert-folder-headers)))))))
+
+(defun mh-copy-line-to-point (msg location)
+  "Copy current message line to a specific location.
+The argument MSG is not used. The message in the current line is copied to
+LOCATION."
+  ;; msg is not used?
+  ;; Copy the current line to the LOCATION in the current buffer.
+  (beginning-of-line)
+  (save-excursion
+    (let ((beginning-of-line (point))
+          end)
+      (forward-line 1)
+      (setq end (point))
+      (goto-char location)
+      (insert-buffer-substring (current-buffer) beginning-of-line end))))
+
+;;;###mh-autoload
+(defun mh-region-to-msg-list (begin end)
+  "Return a list of messages within the region between BEGIN and END."
+  (save-excursion
+    ;; If end is end of buffer back up one position
+    (setq end (if (equal end (point-max)) (1- end) end))
+    (goto-char begin)
+    (let ((result ()))
+      (while (<= (point) end)
+        (let ((index (mh-get-msg-num nil)))
+          (when (numberp index) (push index result)))
+        (forward-line 1))
+      result)))
+
+
+
+;;; Commands to handle new 'subject sequence.
+;;; Or "Poor man's threading" by psg.
+
+(defun mh-subject-to-sequence (all)
+  "Put all following messages with same subject in sequence 'subject.
+If arg ALL is t, move to beginning of folder buffer to collect all messages.
+If arg ALL is nil, collect only messages fron current one on forward.
+
+Return number of messages put in the sequence:
+
+ nil -> there was no subject line.
+ 0   -> there were no later messages with the same subject (sequence not made)
+ >1  -> the total number of messages including current one."
+  (if (not (eq major-mode 'mh-folder-mode))
+      (error "Not in a folder buffer"))
+  (save-excursion
+    (beginning-of-line)
+    (if (or (not (looking-at mh-scan-subject-regexp))
+            (not (match-string 3))
+            (string-equal "" (match-string 3)))
+        (progn (message "No subject line.")
+               nil)
+      (let ((subject (match-string-no-properties 3))
+            (list))
+        (if (> (length subject) 41)
+            (setq subject (substring subject 0 41)))
+        (save-excursion
+          (if all
+              (goto-char (point-min)))
+          (while (re-search-forward mh-scan-subject-regexp nil t)
+            (let ((this-subject (match-string-no-properties 3)))
+              (if (> (length this-subject) 41)
+                  (setq this-subject (substring this-subject 0 41)))
+              (if (string-equal this-subject subject)
+                  (setq list (cons (mh-get-msg-num t) list))))))
+        (cond
+         (list
+          ;; If we created a new sequence, add the initial message to it too.
+          (if (not (member (mh-get-msg-num t) list))
+              (setq list (cons (mh-get-msg-num t) list)))
+          (if (member '("subject") (mh-seq-names mh-seq-list))
+              (mh-delete-seq 'subject))
+          ;; sort the result into a sequence
+          (let ((sorted-list (sort (copy-sequence list) 'mh-lessp)))
+            (while sorted-list
+              (mh-add-msgs-to-seq (car sorted-list) 'subject nil)
+              (setq sorted-list (cdr sorted-list)))
+            (safe-length list)))
+         (t
+          0))))))
+
+;;;###mh-autoload
+(defun mh-narrow-to-subject ()
+  "Narrow to a sequence containing all following messages with same subject."
+  (interactive)
+  (let ((num (mh-get-msg-num nil))
+        (count (mh-subject-to-sequence t)))
+    (cond
+     ((not count)                       ; No subject line, delete msg anyway
+      nil)
+     ((= 0 count)                       ; No other msgs, delete msg anyway.
+      (message "No other messages with same Subject following this one.")
+      nil)
+     (t                                 ; We have a subject sequence.
+      (message "Found %d messages for subject sequence." count)
+      (mh-narrow-to-seq 'subject)
+      (if (numberp num)
+          (mh-goto-msg num t t))))))
+
+;;;###mh-autoload
+(defun mh-delete-subject ()
+  "Mark all following messages with same subject to be deleted.
+This puts the messages in a sequence named subject.  You can undo the last
+deletion marks using `mh-undo' with a prefix argument and then specifying the
+subject sequence."
+  (interactive)
+  (let ((count (mh-subject-to-sequence nil)))
+    (cond
+     ((not count)                       ; No subject line, delete msg anyway
+      (mh-delete-msg (mh-get-msg-num t)))
+     ((= 0 count)                       ; No other msgs, delete msg anyway.
+      (message "No other messages with same Subject following this one.")
+      (mh-delete-msg (mh-get-msg-num t)))
+     (t                                 ; We have a subject sequence.
+      (message "Marked %d messages for deletion" count)
+      (mh-delete-msg 'subject)))))
+
+;;;###mh-autoload
+(defun mh-delete-subject-or-thread ()
+  "Mark messages for deletion intelligently.
+If the folder is threaded then `mh-thread-delete' is used to mark the current
+message and all its descendants for deletion. Otherwise `mh-delete-subject' is
+used to mark the current message and all messages following it with the same
+subject for deletion."
+  (interactive)
+  (if (memq 'unthread mh-view-ops)
+      (mh-thread-delete)
+    (mh-delete-subject)))
+
+;;; Message threading:
+
+(defun mh-thread-initialize ()
+  "Make hash tables, otherwise clear them."
+  (cond
+   (mh-thread-id-hash
+    (clrhash mh-thread-id-hash)
+    (clrhash mh-thread-subject-hash)
+    (clrhash mh-thread-id-table)
+    (clrhash mh-thread-id-index-map)
+    (clrhash mh-thread-index-id-map)
+    (clrhash mh-thread-scan-line-map)
+    (clrhash mh-thread-subject-container-hash)
+    (clrhash mh-thread-duplicates)
+    (setq mh-thread-history ()))
+   (t (setq mh-thread-id-hash (make-hash-table :test #'equal))
+      (setq mh-thread-subject-hash (make-hash-table :test #'equal))
+      (setq mh-thread-id-table (make-hash-table :test #'eq))
+      (setq mh-thread-id-index-map (make-hash-table :test #'eq))
+      (setq mh-thread-index-id-map (make-hash-table :test #'eql))
+      (setq mh-thread-scan-line-map (make-hash-table :test #'eql))
+      (setq mh-thread-subject-container-hash (make-hash-table :test #'eq))
+      (setq mh-thread-duplicates (make-hash-table :test #'eq))
+      (setq mh-thread-history ()))))
+
+(defsubst mh-thread-id-container (id)
+  "Given ID, return the corresponding container in `mh-thread-id-table'.
+If no container exists then a suitable container is created and the id-table
+is updated."
+  (when (not id)
+    (error "1"))
+  (or (gethash id mh-thread-id-table)
+      (setf (gethash id mh-thread-id-table)
+            (let ((message (mh-thread-make-message :id id)))
+              (mh-thread-make-container :message message)))))
+
+(defsubst mh-thread-remove-parent-link (child)
+  "Remove parent link of CHILD if it exists."
+  (let* ((child-container (if (mh-thread-container-p child)
+                              child (mh-thread-id-container child)))
+         (parent-container (mh-container-parent child-container)))
+    (when parent-container
+      (setf (mh-container-children parent-container)
+            (loop for elem in (mh-container-children parent-container)
+                  unless (eq child-container elem) collect elem))
+      (setf (mh-container-parent child-container) nil))))
+
+(defsubst mh-thread-add-link (parent child &optional at-end-p)
+  "Add links so that PARENT becomes a parent of CHILD.
+Doesn't make any changes if CHILD is already an ancestor of PARENT. If
+optional argument AT-END-P is non-nil, the CHILD is added to the end of the
+children list of PARENT."
+  (let ((parent-container (cond ((null parent) nil)
+                                ((mh-thread-container-p parent) parent)
+                                (t (mh-thread-id-container parent))))
+        (child-container (if (mh-thread-container-p child)
+                             child (mh-thread-id-container child))))
+    (when (and parent-container
+               (not (mh-thread-ancestor-p child-container parent-container))
+               (not (mh-thread-ancestor-p parent-container child-container)))
+      (mh-thread-remove-parent-link child-container)
+      (cond ((not at-end-p)
+             (push child-container (mh-container-children parent-container)))
+            ((null (mh-container-children parent-container))
+             (push child-container (mh-container-children parent-container)))
+            (t (let ((last-child (mh-container-children parent-container)))
+                 (while (cdr last-child)
+                   (setq last-child (cdr last-child)))
+                 (setcdr last-child (cons child-container nil)))))
+      (setf (mh-container-parent child-container) parent-container))
+    (unless parent-container
+      (mh-thread-remove-parent-link child-container))))
+
+(defun mh-thread-ancestor-p (ancestor successor)
+  "Return t if ANCESTOR is really an ancestor of SUCCESSOR and nil otherwise.
+In the limit, the function returns t if ANCESTOR and SUCCESSOR are the same
+containers."
+  (block nil
+    (while successor
+      (when (eq ancestor successor) (return t))
+      (setq successor (mh-container-parent successor)))
+    nil))
+
+(defsubst mh-thread-get-message-container (message)
+  "Return container which has MESSAGE in it.
+If there is no container present then a new container is allocated."
+  (let* ((id (mh-message-id message))
+         (container (gethash id mh-thread-id-table)))
+    (cond (container (setf (mh-container-message container) message)
+                     container)
+          (t (setf (gethash id mh-thread-id-table)
+                   (mh-thread-make-container :message message))))))
+
+(defsubst mh-thread-get-message (id subject-re-p subject refs)
+  "Return appropriate message.
+Otherwise update message already present to have the proper ID, SUBJECT-RE-P,
+SUBJECT and REFS fields."
+  (let* ((container (gethash id mh-thread-id-table))
+         (message (if container (mh-container-message container) nil)))
+    (cond (message
+           (setf (mh-message-subject-re-p message) subject-re-p)
+           (setf (mh-message-subject message) subject)
+           (setf (mh-message-id message) id)
+           (setf (mh-message-references message) refs)
+           message)
+          (container
+           (setf (mh-container-message container)
+                 (mh-thread-make-message :subject subject
+                                         :subject-re-p subject-re-p
+                                         :id id :references refs)))
+          (t (let ((message (mh-thread-make-message
+                             :subject subject
+                             :subject-re-p subject-re-p
+                             :id id :references refs)))
+               (prog1 message
+                 (mh-thread-get-message-container message)))))))
+
+(defsubst mh-thread-canonicalize-id (id)
+  "Produce canonical string representation for ID.
+This allows cheap string comparison with EQ."
+  (or (and (equal id "") (copy-sequence ""))
+      (gethash id mh-thread-id-hash)
+      (setf (gethash id mh-thread-id-hash) id)))
+
+(defsubst mh-thread-prune-subject (subject)
+  "Prune leading Re:'s, Fwd:'s etc. and trailing (fwd)'s from SUBJECT.
+If the result after pruning is not the empty string then it is canonicalized
+so that subjects can be tested for equality with eq. This is done so that all
+the messages without a subject are not put into a single thread."
+  (let ((case-fold-search t)
+        (subject-pruned-flag nil))
+    ;; Prune subject leader
+    (while (or (string-match "^[ \t]*\\(re\\|fwd?\\)\\(\\[[0-9]*\\]\\)?:[ \t]*"
+                             subject)
+               (string-match "^[ \t]*\\[[^\\]][ \t]*" subject))
+      (setq subject-pruned-flag t)
+      (setq subject (substring subject (match-end 0))))
+    ;; Prune subject trailer
+    (while (or (string-match "(fwd)$" subject)
+               (string-match "[ \t]+$" subject))
+      (setq subject-pruned-flag t)
+      (setq subject (substring subject 0 (match-beginning 0))))
+    ;; Canonicalize subject only if it is non-empty
+    (cond ((equal subject "") (values subject subject-pruned-flag))
+          (t (values
+              (or (gethash subject mh-thread-subject-hash)
+                  (setf (gethash subject mh-thread-subject-hash) subject))
+              subject-pruned-flag)))))
+
+(defun mh-thread-container-subject (container)
+  "Return the subject of CONTAINER.
+If CONTAINER is empty return the subject info of one of its children."
+  (cond ((and (mh-container-message container)
+              (mh-message-id (mh-container-message container)))
+         (mh-message-subject (mh-container-message container)))
+        (t (block nil
+             (dolist (kid (mh-container-children container))
+               (when (and (mh-container-message kid)
+                          (mh-message-id (mh-container-message kid)))
+                 (let ((kid-message (mh-container-message kid)))
+                   (return (mh-message-subject kid-message)))))
+             (error "This can't happen!")))))
+
+(defun mh-thread-rewind-pruning ()
+  "Restore the thread tree to its state before pruning."
+  (while mh-thread-history
+    (let ((action (pop mh-thread-history)))
+      (cond ((eq (car action) 'DROP)
+             (mh-thread-remove-parent-link (cadr action))
+             (mh-thread-add-link (caddr action) (cadr action)))
+            ((eq (car action) 'PROMOTE)
+             (let ((node (cadr action))
+                   (parent (caddr action))
+                   (children (cdddr action)))
+               (dolist (child children)
+                 (mh-thread-remove-parent-link child)
+                 (mh-thread-add-link node child))
+               (mh-thread-add-link parent node)))
+            ((eq (car action) 'SUBJECT)
+             (let ((node (cadr action)))
+               (mh-thread-remove-parent-link node)
+               (setf (mh-container-real-child-p node) t)))))))
+
+(defun mh-thread-prune-containers (roots)
+  "Prune empty containers in the containers ROOTS."
+  (let ((dfs-ordered-nodes ())
+        (work-list roots))
+    (while work-list
+      (let ((node (pop work-list)))
+        (dolist (child (mh-container-children node))
+          (push child work-list))
+        (push node dfs-ordered-nodes)))
+    (while dfs-ordered-nodes
+      (let ((node (pop dfs-ordered-nodes)))
+        (cond ((gethash (mh-message-id (mh-container-message node))
+                        mh-thread-id-index-map)
+               ;; Keep it
+               (setf (mh-container-children node)
+                     (mh-thread-sort-containers (mh-container-children node))))
+              ((and (mh-container-children node)
+                    (or (null (cdr (mh-container-children node)))
+                        (mh-container-parent node)))
+               ;; Promote kids
+               (let ((children ()))
+                 (dolist (kid (mh-container-children node))
+                   (mh-thread-remove-parent-link kid)
+                   (mh-thread-add-link (mh-container-parent node) kid)
+                   (push kid children))
+                 (push `(PROMOTE ,node ,(mh-container-parent node) ,@children)
+                       mh-thread-history)
+                 (mh-thread-remove-parent-link node)))
+              ((mh-container-children node)
+               ;; Promote the first orphan to parent and add the other kids as
+               ;; his children
+               (setf (mh-container-children node)
+                     (mh-thread-sort-containers (mh-container-children node)))
+               (let ((new-parent (car (mh-container-children node)))
+                     (other-kids (cdr (mh-container-children node))))
+                 (mh-thread-remove-parent-link new-parent)
+                 (dolist (kid other-kids)
+                   (mh-thread-remove-parent-link kid)
+                   (setf (mh-container-real-child-p kid) nil)
+                   (mh-thread-add-link new-parent kid t))
+                 (push `(PROMOTE ,node ,(mh-container-parent node)
+                                 ,new-parent ,@other-kids)
+                       mh-thread-history)
+                 (mh-thread-remove-parent-link node)))
+              (t
+               ;; Drop it
+               (push `(DROP ,node ,(mh-container-parent node))
+                     mh-thread-history)
+               (mh-thread-remove-parent-link node)))))
+    (let ((results ()))
+      (maphash #'(lambda (k v)
+                   (declare (ignore k))
+                   (when (and (null (mh-container-parent v))
+                              (gethash (mh-message-id (mh-container-message v))
+                                       mh-thread-id-index-map))
+                     (push v results)))
+               mh-thread-id-table)
+      (mh-thread-sort-containers results))))
+
+(defun mh-thread-sort-containers (containers)
+  "Sort a list of message CONTAINERS to be in ascending order wrt index."
+  (sort containers
+        #'(lambda (x y)
+            (when (and (mh-container-message x) (mh-container-message y))
+              (let* ((id-x (mh-message-id (mh-container-message x)))
+                     (id-y (mh-message-id (mh-container-message y)))
+                     (index-x (gethash id-x mh-thread-id-index-map))
+                     (index-y (gethash id-y mh-thread-id-index-map)))
+                (and (integerp index-x) (integerp index-y)
+                     (< index-x index-y)))))))
+
+(defsubst mh-thread-group-by-subject (roots)
+  "Group the set of message containers, ROOTS based on subject.
+Bug: Check for and make sure that something without Re: is made the parent in
+preference to something that has it."
+  (clrhash mh-thread-subject-container-hash)
+  (let ((results ()))
+    (dolist (root roots)
+      (let* ((subject (mh-thread-container-subject root))
+             (parent (gethash subject mh-thread-subject-container-hash)))
+        (cond (parent (mh-thread-remove-parent-link root)
+                      (mh-thread-add-link parent root t)
+                      (setf (mh-container-real-child-p root) nil)
+                      (push `(SUBJECT ,root) mh-thread-history))
+              (t
+               (setf (gethash subject mh-thread-subject-container-hash) root)
+               (push root results)))))
+    (nreverse results)))
+
+(defsubst mh-thread-process-in-reply-to (reply-to-header)
+  "Extract message id's from REPLY-TO-HEADER.
+Ideally this should have some regexp which will try to guess if a string
+between < and > is a message id and not an email address. For now it will
+take the last string inside angles."
+  (let ((end (mh-search-from-end ?> reply-to-header)))
+    (when (numberp end)
+      (let ((begin (mh-search-from-end ?< (substring reply-to-header 0 end))))
+        (when (numberp begin)
+          (list (substring reply-to-header begin (1+ end))))))))
+
+(defun mh-thread-set-tables (folder)
+  "Use the tables of FOLDER in current buffer."
+  (flet ((mh-get-table (symbol)
+                       (save-excursion
+                         (set-buffer folder)
+                         (symbol-value symbol))))
+    (setq mh-thread-id-hash (mh-get-table 'mh-thread-id-hash))
+    (setq mh-thread-subject-hash (mh-get-table 'mh-thread-subject-hash))
+    (setq mh-thread-id-table (mh-get-table 'mh-thread-id-table))
+    (setq mh-thread-id-index-map (mh-get-table 'mh-thread-id-index-map))
+    (setq mh-thread-index-id-map (mh-get-table 'mh-thread-index-id-map))
+    (setq mh-thread-scan-line-map (mh-get-table 'mh-thread-scan-line-map))
+    (setq mh-thread-subject-container-hash
+          (mh-get-table 'mh-thread-subject-container-hash))
+    (setq mh-thread-duplicates (mh-get-table 'mh-thread-duplicates))
+    (setq mh-thread-history (mh-get-table 'mh-thread-history))))
+
+(defsubst mh-thread-update-id-index-maps (id index)
+  "Message with id, ID is the message in INDEX.
+The function also checks for duplicate messages (that is multiple messages
+with the same ID). These messages are put in the `mh-thread-duplicates' hash
+table."
+  (let ((old-index (gethash id mh-thread-id-index-map)))
+    (when old-index (push old-index (gethash id mh-thread-duplicates)))
+    (setf (gethash id mh-thread-id-index-map) index)
+    (setf (gethash index mh-thread-index-id-map) id)))
+
+
+
+;;; Generate Threads...
+
+(defun mh-thread-generate (folder msg-list)
+  "Scan FOLDER to get info for threading.
+Only information about messages in MSG-LIST are added to the tree."
+  (save-excursion
+    (set-buffer (get-buffer-create "*mh-thread*"))
+    (mh-thread-set-tables folder)
+    (erase-buffer)
+    (when msg-list
+      (apply
+       #'call-process (expand-file-name mh-scan-prog mh-progs) nil '(t nil) nil
+       "-width" "10000" "-format"
+       "%(msg)\n%{message-id}\n%{references}\n%{in-reply-to}\n%{subject}\n"
+       folder (mapcar #'(lambda (x) (format "%s" x)) msg-list)))
+    (goto-char (point-min))
+    (let ((roots ())
+          (case-fold-search t))
+      (block nil
+        (while (not (eobp))
+          (block process-message
+            (let* ((index-line
+                    (prog1 (buffer-substring (point) (line-end-position))
+                      (forward-line)))
+                   (index (car (read-from-string index-line)))
+                   (id (prog1 (buffer-substring (point) (line-end-position))
+                         (forward-line)))
+                   (refs (prog1 (buffer-substring (point) (line-end-position))
+                           (forward-line)))
+                   (in-reply-to (prog1 (buffer-substring (point)
+                                                         (line-end-position))
+                                  (forward-line)))
+                   (subject (prog1
+                                (buffer-substring (point) (line-end-position))
+                              (forward-line)))
+                   (subject-re-p nil))
+              (unless (gethash index mh-thread-scan-line-map)
+                (return-from process-message))
+              (unless (integerp index) (return)) ;Error message here
+              (multiple-value-setq (subject subject-re-p)
+                (mh-thread-prune-subject subject))
+              (setq in-reply-to (mh-thread-process-in-reply-to in-reply-to))
+              (setq refs (append (split-string refs) in-reply-to))
+              (setq id (mh-thread-canonicalize-id id))
+              (mh-thread-update-id-index-maps id index)
+              (setq refs (mapcar #'mh-thread-canonicalize-id refs))
+              (mh-thread-get-message id subject-re-p subject refs)
+              (do ((ancestors refs (cdr ancestors)))
+                  ((null (cdr ancestors))
+                   (when (car ancestors)
+                     (mh-thread-remove-parent-link id)
+                     (mh-thread-add-link (car ancestors) id)))
+                (mh-thread-add-link (car ancestors) (cadr ancestors)))))))
+      (maphash #'(lambda (k v)
+                   (declare (ignore k))
+                   (when (null (mh-container-parent v))
+                     (push v roots)))
+               mh-thread-id-table)
+      (setq roots (mh-thread-prune-containers roots))
+      (prog1 (setq roots (mh-thread-group-by-subject roots))
+        (let ((history mh-thread-history))
+          (set-buffer folder)
+          (setq mh-thread-history history))))))
+
+;;;###mh-autoload
+(defun mh-thread-inc (folder start-point)
+  "Update thread tree for FOLDER.
+All messages after START-POINT are added to the thread tree."
+  (mh-thread-rewind-pruning)
+  (goto-char start-point)
+  (let ((msg-list ()))
+    (while (not (eobp))
+      (let ((index (mh-get-msg-num nil)))
+        (when (numberp index)
+          (push index msg-list)
+          (setf (gethash index mh-thread-scan-line-map)
+                (mh-thread-parse-scan-line)))
+        (forward-line)))
+    (let ((thread-tree (mh-thread-generate folder msg-list))
+          (buffer-read-only nil)
+          (old-buffer-modified-flag (buffer-modified-p)))
+      (delete-region (point-min) (point-max))
+      (let ((mh-thread-body-width (- (window-width) mh-cmd-note
+                                     (1- mh-scan-field-subject-start-offset)))
+            (mh-thread-last-ancestor nil))
+        (mh-thread-generate-scan-lines thread-tree -2))
+      (mh-notate-user-sequences)
+      (mh-notate-deleted-and-refiled)
+      (mh-notate-seq 'cur mh-note-cur mh-cmd-note)
+      (set-buffer-modified-p old-buffer-modified-flag))))
+
+(defvar mh-thread-last-ancestor)
+
+(defun mh-thread-generate-scan-lines (tree level)
+  "Generate scan lines.
+TREE is the hierarchical tree of messages, SCAN-LINE-MAP maps message indices
+to the corresponding scan lines and LEVEL used to determine indentation of
+the message."
+  (cond ((null tree) nil)
+        ((mh-thread-container-p tree)
+         (let* ((message (mh-container-message tree))
+                (id (mh-message-id message))
+                (index (gethash id mh-thread-id-index-map))
+                (duplicates (gethash id mh-thread-duplicates))
+                (new-level (+ level 2))
+                (dupl-flag t)
+                (force-angle-flag nil)
+                (increment-level-flag nil))
+           (dolist (scan-line (mapcar (lambda (x)
+                                        (gethash x mh-thread-scan-line-map))
+                                      (reverse (cons index duplicates))))
+             (when scan-line
+               (when (and dupl-flag (equal level 0)
+                          (mh-thread-ancestor-p mh-thread-last-ancestor tree))
+                 (setq level (+ level 2)
+                       new-level (+ new-level 2)
+                       force-angle-flag t))
+               (when (equal level 0)
+                 (setq mh-thread-last-ancestor tree)
+                 (while (mh-container-parent mh-thread-last-ancestor)
+                   (setq mh-thread-last-ancestor
+                         (mh-container-parent mh-thread-last-ancestor))))
+               (insert (car scan-line)
+                       (format (format "%%%ss"
+                                       (if dupl-flag level new-level)) "")
+                       (if (and (mh-container-real-child-p tree) dupl-flag
+                                (not force-angle-flag))
+                           "[" "<")
+                       (cadr scan-line)
+                       (if (and (mh-container-real-child-p tree) dupl-flag
+                                (not force-angle-flag))
+                           "]" ">")
+                       (truncate-string-to-width
+                        (caddr scan-line) (- mh-thread-body-width
+                                             (if dupl-flag level new-level)))
+                       "\n")
+               (setq increment-level-flag t)
+               (setq dupl-flag nil)))
+           (unless increment-level-flag (setq new-level level))
+           (dolist (child (mh-container-children tree))
+             (mh-thread-generate-scan-lines child new-level))))
+        (t (let ((nlevel (+ level 2)))
+             (dolist (ch tree)
+               (mh-thread-generate-scan-lines ch nlevel))))))
+
+;; Another and may be better approach would be to generate all the info from
+;; the scan which generates the threading info. For now this will have to do.
+(defun mh-thread-parse-scan-line (&optional string)
+  "Parse a scan line.
+If optional argument STRING is given then that is assumed to be the scan line.
+Otherwise uses the line at point as the scan line to parse."
+  (let* ((string (or string
+                     (buffer-substring-no-properties (line-beginning-position)
+                                                     (line-end-position))))
+         (first-string (substring string 0 (+ mh-cmd-note 8))))
+    (setf (elt first-string mh-cmd-note) ? )
+    (when (equal (elt first-string (1+ mh-cmd-note)) (elt mh-note-seq 0))
+      (setf (elt first-string (1+ mh-cmd-note)) ? ))
+    (list first-string
+          (substring string
+                     (+ mh-cmd-note mh-scan-field-from-start-offset)
+                     (+ mh-cmd-note mh-scan-field-from-end-offset -2))
+          (substring string (+ mh-cmd-note mh-scan-field-from-end-offset))
+          string)))
+
+;;;###mh-autoload
+(defun mh-thread-add-spaces (count)
+  "Add COUNT spaces to each scan line in `mh-thread-scan-line-map'."
+  (let ((spaces (format (format "%%%ss" count) "")))
+    (while (not (eobp))
+      (let* ((msg-num (mh-get-msg-num nil))
+             (old-line (nth 3 (gethash msg-num mh-thread-scan-line-map))))
+        (when (numberp msg-num)
+          (setf (gethash msg-num mh-thread-scan-line-map)
+                (mh-thread-parse-scan-line (format "%s%s" spaces old-line)))))
+      (forward-line 1))))
+
+(defun mh-thread-folder ()
+  "Generate thread view of folder."
+  (message "Threading %s..." (buffer-name))
+  (mh-thread-initialize)
+  (goto-char (point-min))
+  (while (not (eobp))
+    (let ((index (mh-get-msg-num nil)))
+      (when (numberp index)
+        (setf (gethash index mh-thread-scan-line-map)
+              (mh-thread-parse-scan-line))))
+    (forward-line))
+  (let* ((range (format "%s-%s" mh-first-msg-num mh-last-msg-num))
+         (thread-tree (mh-thread-generate (buffer-name) (list range))))
+    (delete-region (point-min) (point-max))
+    (let ((mh-thread-body-width (- (window-width) mh-cmd-note
+                                   (1- mh-scan-field-subject-start-offset)))
+          (mh-thread-last-ancestor nil))
+      (mh-thread-generate-scan-lines thread-tree -2))
+    (mh-notate-user-sequences)
+    (mh-notate-deleted-and-refiled)
+    (mh-notate-seq 'cur mh-note-cur mh-cmd-note)
+    (message "Threading %s...done" (buffer-name))))
+
+;;;###mh-autoload
+(defun mh-toggle-threads ()
+  "Toggle threaded view of folder.
+The conversion of normal view to threaded view is exact, that is the same
+messages are displayed in the folder buffer before and after threading. However
+the conversion from threaded view to normal view is inexact. So more messages
+than were originally present may be shown as a result."
+  (interactive)
+  (let ((msg-at-point (mh-get-msg-num nil))
+        (old-buffer-modified-flag (buffer-modified-p))
+        (buffer-read-only nil))
+    (cond ((and (memq 'unthread mh-view-ops) mh-narrowed-to-seq)
+           (unless (mh-valid-view-change-operation-p 'unthread)
+             (error "Can't unthread folder"))
+           (mh-scan-folder mh-current-folder
+                           (format "%s" mh-narrowed-to-seq)
+                           t)
+           (when mh-index-data
+             (mh-index-insert-folder-headers)))
+          ((memq 'unthread mh-view-ops)
+           (unless (mh-valid-view-change-operation-p 'unthread)
+             (error "Can't unthread folder"))
+           (mh-scan-folder mh-current-folder
+                           (format "%s-%s" mh-first-msg-num mh-last-msg-num)
+                           t)
+           (when mh-index-data
+             (mh-index-insert-folder-headers)))
+          (t (mh-thread-folder)
+             (push 'unthread mh-view-ops)))
+    (when msg-at-point (mh-goto-msg msg-at-point t t))
+    (set-buffer-modified-p old-buffer-modified-flag)
+    (mh-recenter nil)))
+
+;;;###mh-autoload
+(defun mh-thread-forget-message (index)
+  "Forget the message INDEX from the threading tables."
+  (let* ((id (gethash index mh-thread-index-id-map))
+         (id-index (gethash id mh-thread-id-index-map))
+         (duplicates (gethash id mh-thread-duplicates)))
+    (remhash index mh-thread-index-id-map)
+    (cond ((and (eql index id-index) (null duplicates))
+           (remhash id mh-thread-id-index-map))
+          ((eql index id-index)
+           (setf (gethash id mh-thread-id-index-map) (car duplicates))
+           (setf (gethash (car duplicates) mh-thread-index-id-map) id)
+           (setf (gethash id mh-thread-duplicates) (cdr duplicates)))
+          (t
+           (setf (gethash id mh-thread-duplicates)
+                 (remove index duplicates))))))
+
+
+
+;;; Operations on threads
+
+(defun mh-thread-current-indentation-level ()
+  "Find the number of spaces by which current message is indented."
+  (save-excursion
+    (let ((address-start-offset (+ mh-cmd-note mh-scan-date-flag-width
+                                   mh-scan-date-width 1))
+          (level 0))
+      (beginning-of-line)
+      (forward-char address-start-offset)
+      (while (char-equal (char-after) ? )
+        (incf level)
+        (forward-char))
+      level)))
+
+;;;###mh-autoload
+(defun mh-thread-next-sibling (&optional previous-flag)
+  "Jump to next sibling.
+With non-nil optional argument PREVIOUS-FLAG jump to the previous sibling."
+  (interactive)
+  (cond ((not (memq 'unthread mh-view-ops))
+         (error "Folder isn't threaded"))
+        ((eobp)
+         (error "No message at point")))
+  (beginning-of-line)
+  (let ((point (point))
+        (done nil)
+        (my-level (mh-thread-current-indentation-level)))
+    (while (and (not done)
+                (equal (forward-line (if previous-flag -1 1)) 0)
+                (not (eobp)))
+      (let ((level (mh-thread-current-indentation-level)))
+        (cond ((equal level my-level)
+               (setq done 'success))
+              ((< level my-level)
+               (message "No %s sibling" (if previous-flag "previous" "next"))
+               (setq done 'failure)))))
+    (cond ((eq done 'success) (mh-maybe-show))
+          ((eq done 'failure) (goto-char point))
+          (t (message "No %s sibling" (if previous-flag "previous" "next"))
+             (goto-char point)))))
+
+;;;###mh-autoload
+(defun mh-thread-previous-sibling ()
+  "Jump to previous sibling."
+  (interactive)
+  (mh-thread-next-sibling t))
+
+(defun mh-thread-immediate-ancestor ()
+  "Jump to immediate ancestor in thread tree."
+  (beginning-of-line)
+  (let ((point (point))
+        (ancestor-level (- (mh-thread-current-indentation-level) 2))
+        (done nil))
+    (if (< ancestor-level 0)
+        nil
+      (while (and (not done) (equal (forward-line -1) 0))
+        (when (equal ancestor-level (mh-thread-current-indentation-level))
+          (setq done t)))
+      (unless done
+        (goto-char point))
+      done)))
+
+;;;###mh-autoload
+(defun mh-thread-ancestor (&optional thread-root-flag)
+  "Jump to the ancestor of current message.
+If optional argument THREAD-ROOT-FLAG is non-nil then jump to the root of the
+thread tree the message belongs to."
+  (interactive "P")
+  (beginning-of-line)
+  (cond ((not (memq 'unthread mh-view-ops))
+         (error "Folder isn't threaded"))
+        ((eobp)
+         (error "No message at point")))
+  (let ((current-level (mh-thread-current-indentation-level)))
+    (cond (thread-root-flag
+           (while (mh-thread-immediate-ancestor))
+           (mh-maybe-show))
+          ((equal current-level 1)
+           (message "Message has no ancestor"))
+          (t (mh-thread-immediate-ancestor)
+             (mh-maybe-show)))))
+
+(defun mh-thread-find-children ()
+  "Return a region containing the current message and its children.
+The result is returned as a list of two elements. The first is the point at the
+start of the region and the second is the point at the end."
+  (beginning-of-line)
+  (if (eobp)
+      nil
+    (let ((address-start-offset (+ mh-cmd-note mh-scan-date-flag-width
+                                   mh-scan-date-width 1))
+          (level (mh-thread-current-indentation-level))
+          spaces begin)
+      (setq begin (point))
+      (setq spaces (format (format "%%%ss" (1+ level)) ""))
+      (forward-line)
+      (block nil
+        (while (not (eobp))
+          (forward-char address-start-offset)
+          (unless (equal (string-match spaces (buffer-substring-no-properties
+                                               (point) (line-end-position)))
+                         0)
+            (beginning-of-line)
+            (backward-char)
+            (return))
+          (forward-line)))
+      (list begin (point)))))
+
+;;;###mh-autoload
+(defun mh-thread-delete ()
+  "Mark current message and all its children for subsequent deletion."
+  (interactive)
+  (cond ((not (memq 'unthread mh-view-ops))
+         (error "Folder isn't threaded"))
+        ((eobp)
+         (error "No message at point"))
+        (t (mh-delete-msg
+            (apply #'mh-region-to-msg-list (mh-thread-find-children))))))
+
+;; This doesn't handle mh-default-folder-for-message-function. We should
+;; refactor that code so that we don't copy it.
+;;;###mh-autoload
+(defun mh-thread-refile (folder)
+  "Mark current message and all its children for refiling to FOLDER."
+  (interactive (list
+                (intern (mh-prompt-for-folder
+                         "Destination"
+                         (cond ((eq 'refile (car mh-last-destination-folder))
+                                (symbol-name (cdr mh-last-destination-folder)))
+                               (t ""))
+                         t))))
+  (cond ((not (memq 'unthread mh-view-ops))
+         (error "Folder isn't threaded"))
+        ((eobp)
+         (error "No message at point"))
+        (t (mh-refile-msg
+            (apply #'mh-region-to-msg-list (mh-thread-find-children))
+            folder))))
+
+(provide 'mh-seq)
+
+;;; Local Variables:
+;;; indent-tabs-mode: nil
+;;; sentence-end-double-space: nil
+;;; End:
+
+;;; mh-seq.el ends here