The Overpath Method
We saw in Chapter XII that the cohomology group H 2 (S, G) can be computed by means of functions of two variables in S, namely, symmetric 2-cocycles. The overpath method computes H 2 (S, G) by means of functions of one variable, one for every defining relation of S in any suitable presentation of S. This makes the computation of H 2 (S, G) a finite task whenever S is finitely generated.
KeywordsAbelian Group Positive Relation Commutative Semigroup Surjective Homomorphism Commutative Monoid
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