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<p>map reduces to the one of boundary through the construction of the <a href="page.php?w=Mapping_cone_%28homological_algebra%29">cone</a> of a chain map.</p>

<p><big>Chain homotopy</big></p>
<p>A chain homotopy offers a way to relate two chain maps that induce the same map on homology groups, even though the maps may be different. Given two chain complexes A and B, and two chain maps ''f'', ''g'' : ''A'' -> ''B'', a <b>chain homotopy</b> is a sequence of homomorphisms ''h''<sub>''n''</sub> : ''A''<sub>''n''</sub> -> ''B''<sub>''n''+1</sub> such that 1=''hd''<sub>''A''</sub></p><p>
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