  Using the works of Gervais, Harer, Hatcher and Thurston and others, we show
that the mapping class group of a compact orientable surface has a presentation
so that the generators are the set of all Dehn twists and the relations are
supported in subsurfaces homeomorphic to the one-holed torus or the four-holed
sphere. It turns out that all the relations were discovered by Dehn in 1938.
