Schur multiplier of an abelian group (source code)

= Schur multiplier of an abelian group

For an <abelian group> $A$,
$$
M(A)\cong\bigwedge^2A.
$$
For a finite direct sum of cyclic groups this gives one summand $C_{\gcd(m,n)}$ for every pair $C_m,C_n$.