Vol. 128, No. 1, 1987

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On a cohomology theory based on hyperfinite sums of microsimplexes

Rade Živaljević

Vol. 128 (1987), No. 1, 201–208
Abstract

In this note we investigate a cohomology theory H#(X,G), defined by M. C. McCord, which is dual to a homology theory based on hyperfinite chains of miscrosimplexes. We prove that if X is a locally contractible, paracompact space then H#(X,G) Hč#(X,Hom(Z,G)) where Hč# is the Čech theory. Nonstandard analysis, particularly the Saturation Principle, is used in this proof in essential way to construct a fine resolution of the constant sheaf X × Hom(Z,Z). This gives a partial answer to a question of McCord. Subsequently, we prove a proposition from which it is deduced that Hom(Z,Z) = {0} i.e. H#(X,Z) = {0} if X is paracompact and locally contractible. At the end we briefly discuss a related cohomology theory which is obtained by application of the internal (rather than external) Hom(,G) functor.

Mathematical Subject Classification 2000
Primary: 55N05
Secondary: 03H05, 54J05
Milestones
Received: 1 December 1985
Published: 1 May 1987
Authors
Rade Živaljević