% Fichier ex4.8.4-7.tex - Ch. Rolland/O Reilly France
\documentclass{article}
\usepackage[latin1]{inputenc}
\usepackage{amsmath}
\begin{document}
$$
F\times\triangle[n-1]
  \xrightarrow[\partial_0\alpha(b)]{}
E^{\partial_0b}
$$
\end{document}
