I have a topological space X and two disjoint, closed subspaces Y and Z of X. I believe that in this situation, for any abelian sheaf F on X and any p∈N, there is a natural isomorphism
HpY(X,F)⊕HpZ(X,F)→HpY∪Z(X,F)
between local cohomology groups. I can obtain this by taking an injective resolution 0→F→I∙ of F, and constructing by hand a split exact sequence of complexes of sheaves
0→ΓY(X,I∙)→ΓY∪Z(X,I∙)→ΓZ(X,I∙)→0
and then passing to cohomology. I am certain that this is completely standard and well known; could someone please point me to a (preferably modern) reference for this result?
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Source : Link , Question Author : user90358 , Answer Author : Community