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The definition given here (which really does not belong on a disambiguation page) gives an 8 digit number with the claim that this is an ISBN number, but ISBN numbers always have more than 8 digits. Does anyone have any idea what the reference is? Rick Norwood ( talk) 14:12, 29 December 2010 (UTC) reply

Cocycle of a group action should be covered. See for instance: stackexchange, a lecture. Surely, better sources exist; but I am not an expert here. Boris Tsirelson ( talk) 08:14, 24 August 2019 (UTC) reply