Second microlocal ellipticity and propagation of conormality for semilinear wave equations (Q1180629)

The author considers three problems on the propagation of conormal singularities for semilinear wave equations: the evolution of two simply tangent waves, the interaction of three conormal waves, and the evolution of one wave with a cusp singularity. He uses quasihomogeneous blow-ups to reduce the geometries to normal crossing and show that the lift of the operator by these blow-down maps is elliptic in some directions of the compressed cotangent bundle of the blown-up manifold. This leads to a strengthening of the previously known results and a simplification of their proofs.