How to generate k+1 length strings from a list of k length strings?

[bearophileHUGS at lycos.com]

Boris Borcic:
> > I don't do challenges.
>
> Pfff... and you don't do real debates either.

Different nations have different values and different cultures, in mine
challenges are often seen as things for children, and a waste of time
for adults (probably in USA challenges are appreciated more).

Bye,
bearophile