In 1980, Albert Fathi asked whether the group of area-preserving
homeomorphisms of the 2-disc that are the identity near the boundary
is a simple group. In this paper, we show that the simplicity of this
group is equivalent to the following fragmentation property in the group
of compactly supported, area preserving diffeomorphisms of the plane:
there exists a constant m such that every element supported on a disc
D is the product of at most m elements supported on topological discs
whose area are half the area of D.