RE: how to extend `C-x 8` keymap?

[Drew Adams]

> How can I (presumably in init.el) extend my `C-x 8` keymap?
>
> sequence  produce  as does (currently)
> --------  -------  ------------------------------------
> C-x 8 d   d        C-x 8 RET GREEK SMALL LETTER DELTA
> C-x 8 D   ?        C-x 8 RET GREEK CAPITAL LETTER DELTA
> 
> Currently those sequences are undefined.

Try this:

(define-key iso-transl-ctl-x-8-map "d" [?X])
(define-key iso-transl-ctl-x-8-map "D" [?Y])

But instead of X and Y you need to use the actual chars you want.