Upper and lower solutions for an integral boundary problem with two different orders (p,q)-fractional difference

In this paper, a (p,q)-fractional nonlinear difference equation of different orders is considered and discussed. With the help of (p,q)-calculus for integrals and derivatives properties, we convert the main integral boundary value problem (IBVP) to an equivalent solution in the form of an integral equation, we use the upper-lower solution technique to prove the existence of positive solutions. We present an example of the IBVP to apply and demonstrate the results of our method.