Suppose 
 and 
 are two chain homomorphisms. Then a chain homotopy
 is given by a sequence of maps
such that
where 
 denotes the boundary operator.
 
	    
	
    
Suppose 
 and 
 are two chain homomorphisms. Then a chain homotopy
 is given by a sequence of maps
such that
where 
 denotes the boundary operator.
This entry contributed by Todd Rowland
Rowland, Todd. "Chain Homotopy." From MathWorld--A Wolfram Resource, created by Eric W. Weisstein. https://mathworld.wolfram.com/ChainHomotopy.html