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Let $G$ be an (additive) abelian group. Is there a concise, standard term for the order of the kernel $K$ of the endomorphism $g\mapsto 2g$? Or alternatively, for the index of $K$?

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Order of 2-torsion of G. – Georges Elencwajg Mar 15 '10 at 13:30
Thanks! Now I need to type some more because the software won't let me post a comment as short as "Thanks!" – Mark Meckes Mar 15 '10 at 14:04

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