(defun delete-indentation (&optional arg)
  "Join this line to previous and fix up whitespace at join.
If there is a fill prefix, delete it from the beginning of this line.
With argument, join this line to following line."
  (interactive "*P")
  (let ((return-point (point))
        (return-col (if (not arg) (- (point-at-eol) (point)))))
   (beginning-of-line)
   (if arg (forward-line 1))
   (if (eq (preceding-char) ?\n)
       (progn
 	(delete-region (point) (1- (point)))
 	;; If the second line started with the fill prefix,
 	;; delete the prefix.
 	(if (and fill-prefix
 		 (<= (+ (point) (length fill-prefix)) (point-max))
 		 (string= fill-prefix
 			  (buffer-substring (point)
 					    (+ (point) (length fill-prefix)))))
 	    (delete-region (point) (+ (point) (length fill-prefix))))
 	(fixup-whitespace)
    (if return-col
      (goto-char (- (point-at-eol) return-col))
     (goto-char return-point))))))

(defun my-join-lines (&optional arg)
  "Join multiple lines, forward or backwards.

By default, joins forward one line (the standard `join-lines',
an alias for `delete-indentation', and bound by default to M-^,
joins backward by default).

With a prefix argument joins that number of lines in +/- direction.

With a region selected, joins all lines in the region."
  (interactive "p")
  (let ((return-point (point))                           ; ┃
        return-col)                                      ; ┃
    (if (use-region-p)
      (let ((begin (region-beginning)))
        (when (= (point) (region-end))                   ; ┃
          (setq return-col (- (point-at-eol) (point))))  ; ┃
        (goto-char (region-end))
        (while (> (point-at-bol) begin)
          (join-line)))
     (if arg
       (if (> arg 0)
         (dotimes (i arg) (join-line t))
        (setq return-col (- (point-at-eol) (point)))     ; ┃
        (dotimes (i (- 0 arg)) (join-line)))
      (join-line t)))
    (if return-col                                       ; ┃
      (goto-char (- (point-at-eol) return-col))          ; ┃
     (goto-char return-point))))                         ; ┃