ABSTRACT
This states that certain subspaces U ⊂ A may be cut out or excised from the space without affecting the relative homology modules. More precisely, the inclusion map (X – U, A – U) → (X, A) is called an excision if it induces an isomorphism H q ( X − U , A − U ) → H q ( X , A ) https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780429502408/295d3acc-dfa3-4421-a2d3-a9c22ffb681c/content/eq316.tif"/>
