The work of Hans Lewy (1904-1988) has had a profound influence in the direc- tion of applied mathematics and partial differential equations, in particular, from the late 1920s. We are all familiar with two of the particulars. The Courant-Friedrichs- Lewy condition (1928), or CFL condition, was devised to obtain existence and ap- proximation results. This condition, relating the time and spatial discretizations for finite difference schemes, is now universally employed in the simulation of solutions of equations describing propagation phenomena. His example of a linear equation with no...