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when toggle format what by license comment
Feb 11, 2016 at 14:16 comment added Fedor Petrov Yes, I see. Unfortunately, I do not know references.
Feb 11, 2016 at 14:11 comment added Salvo Tringali Thanks, and +1. However, let me note that I asked for a reference, not for a proof. The more general the case covered by the reference is, the happier I am.
Feb 11, 2016 at 14:03 history answered Fedor Petrov CC BY-SA 3.0