Relates cohomology with coefficients in G to integral homology via a natural split short exact sequence involving Hom and Ext. Splits but the splitting is not natural. Analogue for homology expresses H_*(X; G) via H_*(X) and Tor.
Relates cohomology with coefficients in G to integral homology via a natural split short exact sequence involving Hom and Ext. Splits but the splitting is not natural. Analogue for homology expresses H_*(X; G) via H_*(X) and Tor.