Decreasing diagrams and coherent presentations

We show how decreasing diagrams introduced in the theory of rewriting systems can be used to prove coherence type theorems in category theory. We apply this method to describe a coherent presentation of the $0$-Hecke monoid $\mathcal{H}(\Sigma_n)$ of the symmetric group $\Sigma_n$, i.e. a presentation by generators, relations, and relations between relations.