Is a (say, projective) resolution (of a module) consisting entirely of zero modules considered to have a length (of zero) at all? I think this possibility causes problems in some books.
closed as off-topic by Ricardo Andrade, Andrey Rekalo, Stefan Kohl, Chris Godsil, David White Nov 28 '13 at 15:56
This question appears to be off-topic. The users who voted to close gave this specific reason:
- "This question does not appear to be about research level mathematics within the scope defined in the help center." – Ricardo Andrade, Andrey Rekalo, Stefan Kohl, Chris Godsil, David White