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For questions about projective modules over a ring and projective objects in related categories.

1 vote
0 answers
229 views

A question concerning a short exact sequence with an action

Let $A$ and $D$ be two non-trivial abelian groups and $B,C$ be two non-abelian groups. Also, let $C$ is a free group and acts on $A,B,D$. Let $0\to A \xrightarrow{f}B\xrightarrow{g}C\to 0$ be a s …
MHenry's user avatar
  • 139
3 votes
1 answer
425 views

A projective (or free) $\mathbb{Z}\pi_1$-module

Suppose that $Z$ is a finite wedge of spheres containing circles and there exist maps $f:Y\to Z$ and $g:Z\to Y$ so that $g\circ f\simeq 1_Y$. Assume that there exists a map $h:X\to Y$ which induces …
MHenry's user avatar
  • 139