Pontryagin’s condition method of resolving functions set-valued mapping метод розв’язуючих функцій ситуація оточення теорема Пшеничного умова Понтрягіна Apollonius circle Caratheodory set Conflict-controlled process Krasovskii’ extremal aiming rule Pontryagin–Mishchenko problem Pshenichnyi theorem Pshenichnyi’ theorem adjoint state bypass maneuver method collision avoidance compact with a smooth border conflict-controlled process conflict-controlled processes descriptor system deviation in direction differential algebraic equation encirclement situation environment situation group and sequential pursuit impulse intensities impulse system measurable selection method of invariant subspaces