There is more than one way to do it...
Thanks very much for your help (and also for the benchmarking). I did not think that my question would create such a competition ;)
I will need some time to digest some piece of code before understand it, especially the solutions provided by skeeve.

In reply to Re^2: Common elements of a hash of hashes by Anonymous Monk
in thread Common elements of a hash of hashes by Anonymous Monk

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