Past exam of the mathematics course of the University of Cambridge 2020 ii Paper 4 21F c Solution Created 2026-09-24 Updated 2026-09-29
No. Here is the pair of pants, and part (b) gives , whereasIf made homotopic to the identity map of the torus, functoriality of homology and homotopy invariance of homology would giveon . But factors through the zero group , so the left side is zero while the right side is the identity on , a contradiction.