searching a value of a dict (each value is a list)

[bearophileHUGS at lycos.com]

Jeremy C B Nicoll:
> The code someone else posted to reverse the keys is all very well, but
> surely hugely wasteful on cpu, maybe storage, and elapsed time.

If you are talking about my D code then I know it, the creation of the
first dict has to be skipped, if possible... The code I have posted
must be adapted.

Bye,
bearophile