Thank you all for you advice. You helped to set me on the track. But
it is indeed a rather difficult read for me. My head dizzles is still
a bit dizzling.

Below are my very first steps in C: a version of `find-if' as a
starter. I'd appreciate any comment. (Did I miss something important,
for example?)

One thing that I noticed is that my `find-if' causes an infinite loop,
when applied to a recursive (?) list, à la:

(setq my-list (list 'alpha 'beta 'gamma))

(setcdr (cddr my-list) my-list)

(find-if (lambda (elt) (eq elt 'zeta)) my-list)

I couldn't think of a remedy for this. How could I solve this problem?
OTOH this happens to `copy-sequence', too. So maybe this is o.k.?