A skateboarder grinds along a pipe beneath a fire escape.
The skateboarder is skipping instead of skateboarding.
If the skateboarder grinds, then he is indeed skateboarding.
exists e1 x1 x2 x3 x4.(beneath(e1,x3) & n_escape(x3) & of(x3,x4) & n_fire(x4) & along(e1,x2) & n_pipe(x2) & Actor(e1,x1) & v_grind(e1) & n_skateboarder(x1))
exists e1 x1.(n_skateboarder(x1) & -exists e2 x2.(of(e1,e2) & Actor(e2,x2) & v_skateboard(e2)) & Actor(e1,x1) & v_skip(e1))