Published online by Cambridge University Press: 11 October 2006
Let  $\Lambda $  be a Lagrangian submanifold of  $T^{*}X$
  be a Lagrangian submanifold of  $T^{*}X$  for some closedmanifold X. Let  $S(x,\xi )$
  for some closedmanifold X. Let  $S(x,\xi )$  be a generating function for  $\Lambda $
  be a generating function for  $\Lambda $  whichis quadratic at infinity, and let W(x) be the corresponding graph selectorfor  $\Lambda ,$
  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  $X_{0}\subset X$
  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  $X\backslash X_{0}$
  of measure zero such that W is Lipschitzcontinuous on X, smooth on  $X\backslash X_{0}$  and  $(x,\partial W/\partialx(x))\in \Lambda $
  and  $(x,\partial W/\partialx(x))\in \Lambda $  for  $X\backslash X_{0}.$
  for  $X\backslash X_{0}.$  Let H(x,p)=0 for  $(x,p)\in\Lambda$
  Let H(x,p)=0 for  $(x,p)\in\Lambda$  . Then W is a classical solution to  $H(x,\partial W/\partialx(x))=0$
 . Then W is a classical solution to  $H(x,\partial W/\partialx(x))=0$  on  $X\backslash X_{0}$
  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.
  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.
 problem, to appear in J. Math. Anal & Appl. (August 2005).
                  
                problem, to appear in J. Math. Anal & Appl. (August 2005). control of nonlinear systems: differential games and viscosity solutions. 
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