EDB — 1RY

[1RY]In the above hypotheses, assuming that \(\frac{\partial {}F}{\partial {y}} {\gt} 0\) and \(\frac{\partial {}^ 2F}{\partial {aa}}{\gt}0\), show that the envelope graph \(g\) is locally the ”edge” of the union of the graphs \(f_ a\) (in the sense that \(g(x)≥ f_ a(x)\) with equality for only one \(a\)).