diagonal of a bisimplicial set

**(diagonal)**

For $X_{\bullet,\bullet}$ a bisimplicial set, its **diagonal** is the simplicial set that is the precomposition with $(Id, Id) : \Delta^{op} \to \Delta^{op} \times \Delta^{op}$, i.e. the simplicial set with components.

$d(X)_n = X_{n,n}
\,.$

See also diagonal.

Revised on April 18, 2013 18:50:16
by Tim Porter
(95.147.236.226)