algebraic3d
solid cube = plane (0, 0, 0; 0, 0, -1)
         and plane (0, 0, 0; 0, -1, 0)
         and plane (0, 0, 0; -1, 0, 0)
         and plane (1, 1, 1; 0, 0, 1)
         and plane (1, 1, 1; 0, 1, 0)
         and plane (1, 1, 1; 1, 0, 0);
solid cutplane = plane (0.5, 0, 0; -1, 0, 0);

solid right = cube and cutplane;
solid left = cube and not cutplane;

tlo right -col=[1,0,0];
tlo left -col=[0,0,1];