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

[bearophileHUGS at lycos.com]

> I think there can be written more readable code. For my programs I
> usually prefer simpler code, that (if possible) even a children can
> understand. So I can debug, modify and improve it better & faster.

Debugged:
I think it can be written more readable code.
In this newsgroup sometimes I have tried to post 'clever' code, but for
my programs I (if possible) prefer simpler code, that even a child can
understand. So I can debug, modify and improve it faster.

Sorry, I was tired,
bearophile