# Contents

## Idea

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

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

In terms of presentations this means:

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

For background and details see fibration sequence.

Revised on November 17, 2013 01:55:32 by Urs Schreiber (82.113.98.128)