Published online by Cambridge University Press: 11 October 2006
Let $\Lambda $ be a Lagrangian submanifold of $T^{*}X$ for some closedmanifold X. Let $S(x,\xi )$ be a generating function for $\Lambda $ whichis quadratic at infinity, and let W(x) be the corresponding graph selectorfor $\Lambda ,$ in the sense of Chaperon-Sikorav-Viterbo, so that thereexists a subset $X_{0}\subset X$ of measure zero such that W is Lipschitzcontinuous on X, smooth on $X\backslash X_{0}$ and $(x,\partial W/\partialx(x))\in \Lambda $ for $X\backslash X_{0}.$ Let H(x,p)=0 for $(x,p)\in\Lambda$ . Then W is a classical solution to $H(x,\partial W/\partialx(x))=0$ on $X\backslash X_{0}$ and extends to a Lipschitz function on thewhole of X. Viterbo refers to W as a variational solution. We prove that W is also a viscosity solution under some simple and natural conditions.We also prove that these conditions are satisfied in many cases, includingcertain commonly occuring cases where H(x,p) is not convex in p.