Wave Front Sets, H-Measures

Abstract

In the summer of 1972, I listened to a conference on partial differential equations in Jerusalem, Israel. It was the first time that I heard Lars HÖNORMANDER talk,¹ and his work was related to lacunas,² which is about identifying the exact support of the elementary solution E of an hyperbolic equation having support in t ≥ 0; he introduced a new notion, the wave front set of a distribution T Є D’(Ω),³ denoted WF(T ) and also called the essen- tial singular support of T , for which he proved propagation results, which enabled him to identify WF(E) (but not the support of E).⁴