On Equations of Minimal Surface Type

Let D be a plane domain, r its boundary. Let s* be a continuous function defined on r. The function s* then determines a curve T in (x, y, so) space of which r is a simply covered projection. Such a curve is said to satisfy a threepoint condition with constant A provided that any plane which intersects it in three or more points has maximum inclination less than A (cf [1]). The concept of the three point condition has been an essential feature in the theory of quasi-linear elliptic partial differential equations in two independent variables