gistfile1.el

  (defun notmuch-show-previous-thread (&optional show-next)
    "Move to the previous item in the search results, if any."
    (interactive "P")
    (let ((parent-buffer notmuch-show-parent-buffer))
      (notmuch-kill-this-buffer)
      (when parent-buffer
        (switch-to-buffer parent-buffer)
        (notmuch-search-previous-thread)
        (if show-next
            (notmuch-search-show-thread)))))