Thursday, September 12, 2019

field theory - In what vector space does Dedekind's lemma live?



Dedekind's lemma in field theory says this:




Let E and L be fields, and σ1,,σn:EL be distinct field homomorphisms. Then σ1,,σn are L-linearly independent, that is ni=1aiσi=0,aiL(i)ai=0,





Is there an L-vector space in which this linear independence takes place? All field homomorphisms from E to L don't constitute a vector space because there is no neutral element in this set. Also, the sum of two homomorphisms may not be a homomorphism. If charL=2, and σ:EL is a field homomorphism, then σ+σ=0 isn't a field homomorphism. I'm not really sure when the sum of two homomorphisms is again a homomorphism. Also, I'm not sure when the additive inverse of a homomorphism is again a homomorphism. Could you please help with these questions?


Answer



The space of all additive homomorphisms from E to L (E and L are considered as abelian groups w.r.t. addition). If f is such homomorphism and aL, then af maps x to af(x).


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