how to get the expression in an operator in maple?

Question

I am deriving an HJB type PDE with Maple like this:

eq1 := diff(U(t, q), t) + lambda*sup(h(delta)*(U(t, q - 1) - U(t, q)) + (1 - h(delta))*(U(t, q) - U(t, q))+delta, delta) = 0;

how can I get the epression in sup operator? I have tried

indets(eq1, function);
select(has,eq1,delta);

but fails

what I want is to get

eq2:=h(delta)*(U(t, q - 1) - U(t, q)) + (1 - h(delta))*(U(t, q) - U(t, q))+delta

Answer 1

eq1 := diff(U(t, q), t)
       + lambda*sup(h(delta)*(U(t, q - 1) - U(t, q))
                    + (1 - h(delta))*(U(t, q) - U(t, q))+delta,
                    delta) = 0:

op( [1,1], indets(eq1,specfunc(sup)) );

        h(delta) (U(t, q - 1) - U(t, q)) + delta