most recent 30 from http://mathoverflow.net 2013-05-24T14:52:59Z http://mathoverflow.net/feeds/question/30481 http://www.creativecommons.org/licenses/by-nc/2.5/rdf http://mathoverflow.net/questions/30481/f0-0-f-additive-functor expmat 2010-07-04T04:27:43Z 2010-07-06T14:05:47Z

<p>If I define an additive functor to be a functor on abelian categories such that the action of F on Hom(A,B) is a group homomorphism, do I necessarily have that F(zero object) = zero object?</p>

http://mathoverflow.net/questions/30481/f0-0-f-additive-functor/30779#30779 t3suji 2010-07-06T14:05:47Z 2010-07-06T14:05:47Z

<p>Since the OP asked for a detailed answer:</p> <p>Let $A$ be an object of an abelian (or additive) category. Then $A$ is a zero object if and only if the zero endomorphism is the identity endomorphism (and then $Hom(A,A)$ is the zero ring). If $F$ is any functor, it sends the identity morphism of $A$ to the identity morphism of $F(A)$. If in addition $F$ is additive (no pun intended), it also sends the zero morphism to the zero morphism. Thus $F(0)$ is a zero object.</p> <p>Another exercise in the similar spirit: show that additive functor is additive on objects: it sends finite direct sums to direct sums. (Your question is the particular case of empty direct sum.)</p>