I work on Stochastic Control theory and BSDE's for my research. In my research, I characterized the set I am interested in as the level set of a function which is a viscosity solution to nonlinear PDE (HJB Equation). I was able to prove that this set is unbounded.(Its a 2 dimensional set)
$D(t,x) = \left\{(y_1,y_2) : w(t,x,y_1,y_2)=0 \right\}$ where $w$ is the solution to HJB equation.
Now, let $h(t,x,y_1) = \sup \left\{y_2 : w(t,x,y_1,y_2) = 0 \right\}$. Are there any techniques to characterize $h$ as solution to some PDE.
Thanks