A cochain complex is a sequence of abelian groups or modules 
with homomorphisms 
satisfying 
. Its 
th cohomology group is
.
Cochain Complex
See also
Chain Complex, Cohomology Group, HomomorphismExplore with Wolfram|Alpha
References
Hatcher, A. Algebraic Topology. Cambridge, England: Cambridge University Press, 2002.Cite this as:
Weisstein, Eric W. "Cochain Complex." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/CochainComplex.html