Relative cycle
= Relative cycle
{title2=$\partial b\in C_{n-1}(A)$}
A relative cycle for $A\subset B$ is a chain $b\in C_n(B)$ whose boundary lies in $A$. Equivalently its coset is a <homological cycle> in $C_*(B,A)$. Unlike an absolute cycle, its boundary need not be zero. It represents a <relative homology class>.