The linearised theory of supersonic flow is applied to a plane wing with a pointed apex whose leading edge is subsonic near the apex but supersonic further outboard. The change in character of the leading edge may occur either where the edge is kinked or at a point where its slope is continuous. In each case, the theoretical pressure field due to incidence is found to be singular along the downstream, outward-going Mach line through the point at which the edge changes character. The form of the singularity is different for the two cases, and somewhat unexpected. Measurements of the pressure on a plane wing with a curved, mixed leading edge showed no abrupt variation near the Mach line on which the singular behaviour was predicted.