Re: ¬ notation for not? Ref: Add a couple cells to lisp-prettify-symbols-alist

[Stefan Monnier <monnier@iro.umontreal.ca>]

> What if spaces inside of a sexp, under a prettified symbol, could be prettified too? So I'd see
>
>     (∧ x
>        y
>        z)
>
> but the buffer would really contain
>
>     (and x
>          y
>          z)

Sounds good.  Not sure how to do it reliably, tho:
- how do we find the set of lines that are affected (something like
  forward-sexp could work for the above case)?
- how do we distinguish between lines that are "aligned" and lines which
  are merely indented by a fixed amount?

It might be even possible to make align.el handle alignment correctly
for some of these cases.  E.g. for

    (and x
         (y    45)
         (toto 46))

E.g. by tweaking `current-column` so that it counts the "and displayed
as ∧" as 3 columns rather than 1 (following the same idea as used for
invisible text, where `current-column` currently counts it as
non-invisible if it is displayed as an ellipsis).


        Stefan