Re: Making a key undefined again

[Gregory Heytings]

> Actually, it didn't make it clear for me.  I hope I understand the 
> differences between an `undefined` binding, a `nil ` binding, and no 
> binding at all, but I don't know why unsetting a key is important and 
> even less when unsetting it by making it have no binding at all is 
> necessary.

I'm not sure I understand what Jonas wants, but here's what I understood:

1. (define-key lisp-interaction-mode-map "\C-j" nil)

means that in *scratch* C-j becomes electric-newline-and-maybe-indent (in 
global-map);

2. (define-key lisp-interaction-mode-map "\C-j" #'undefined)

means that in *scratch* C-j displays "C-j is undefined";

3. (define-key lisp-interaction-mode-map "\C-j" (lambda () (interactive)))

means that in *scratch* C-j does nothing.