nLab
long exact sequence of homotopy groups

Contents

Idea

For YZY \to Z a morphism of pointed ∞-groupoids and XYX \to Y its homotopy fiber, there is a long exact sequence of homotopy groups

π n+1(Z)π n(X)π n(Y)π n(Z)π n1(X). \cdots \to \pi_{n+1}(Z) \to \pi_n(X) \to \pi_n(Y) \to \pi_n(Z) \to \pi_{n-1}(X) \to \cdots \,.

In terms of presentations this means:

for YZY \to Z a fibration in the ordinary model structure on topological spaces or in the model structure on simplicial sets, and for XYX \to Y the ordinary fiber of topological spaces or simplicial sets, respectively, we have such a long exact sequence.

For background and details see fibration sequence.

References

The observation of long exact sequences of homotopy groups for homotopy fiber sequences originates (according to Switzer 75, p. 35) in

  • M. G. Barratt, Track groups I, II. Proc. London Math. Soc. 5, 71-106, 285-329 (1955).

The first exhaustive study of these is due to

  • Dieter Puppe, Homotopiemengen und ihre induzierten Abbildungen I, Math. Z. 69, 299-344 (1958).

whence the terminology Puppe sequences.

Textbook accounts include

See also

Revised on May 10, 2016 08:00:13 by Urs Schreiber (131.220.184.222)