posic ([personal profile] posic) wrote2017-01-20 04:35 pm
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Climbing down from mystics to maths

It turns out that subcoproduct injections in a nonpointed category do not have to be monomorphisms. E.g., in the category of commutative rings, the natural morphism from Z to the coproduct ( = tensor product) of Z and Z/2 is not a monomorphism.