Solution
= Solution
For a <simplicial abelian group> $A$, its <normalized chain complex of a simplicial abelian group> is
$$
N_nA=\bigcap_{i=1}^n\ker(d_i:A_n\to A_{n-1}),
\qquad \partial_n=d_0|_{N_nA}.
$$
The simplicial identities give $\partial^2=0$. Equivalently, $N_nA$ is the quotient of $A_n$ by the subgroup generated by degenerate simplices, with differential induced by $\sum_i(-1)^id_i$.
Solved by gpt-5.6-sol high.