static void CollectVariables(Request.Expr e, Dictionary <string, Variable> vars, GLS.Solver solver)
{
if (e.variable != null && !vars.ContainsKey(e.variable))
{
vars[e.variable] = solver.MakeNumVar(0.0, double.PositiveInfinity, e.variable);
}
if (e.left != null)
{
CollectVariables(e.left, vars, solver);
}
if (e.right != null)
{
CollectVariables(e.right, vars, solver);
}
}