A necessary optimality condition of the Pontryagin maximum principle type in one problem of optimal control of a system with distributed parameters

We consider a variable-structure optimal control problem described in different domains by hyperbolic integro-differential equation and Volterra integral equation, respectively. The quality functional is terminal. A formula for the increment of criterion constructed an analogue L.S. Pontryagin's maximum principle proved investigating on special McShane-type variations.