> The sequences set using ctrl-[ work, but using f11 I get the sequence
> ctrl[[23"  from od-cb.  xev gives for f11 a keycode 35 (keysym
> 0xffc8, F11).  xev for ctrl-[ gives a keycode 97 (keysym 0xffe3,
> Control_L) followed by a keycode 172 (keysym 0x5b, bracketleft).

It appears that your F11 is not, after all, the Escape you thought it
was.  If you've meddled with the xmodmap settings for keycode 35, this
is probably your fault; if not, it's the X server's fault (if fault it
truly is).

> If the ctrl-[ works and not the f11, in X, then something is not
> passing the codes correctly to vi, while in X?

FSVO "correctly", yes.  If F11 is the key people expect to press for
escape, then keycode 35 should have Escape as its keysym, not F11.  Why
this is not so is the question.

As a workaround, you can use xmodmap to put Escape, instead of F11, on
keycode 35.  But you really shouldn't have to do that.

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