Question: How can i solve a nonlinear pde in maple?

How can i solve for G(p,q,r,t) in the following pde

diff(G(p, q, r, t), t) = {lambda*(p-1)+gamma*(r-1)}*G(p, q, r, t)+delta*(1-p)*(diff(G(p, q, r, t), p))+kappa*(N*r-q)*(diff(G(p, q, r, t), q))+mu*(1-r)*(diff(G(p, q, r, t), r))+beta*(q*e^(-`ρτ`)-p*r)*(diff(G(p, q, r, t), r, p))

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