A man does a bicycle trick on a concrete obstacle.
A man is skateboarding.
A man can not be skateboarding and also doing a bicycle trick.
exists e1 s1 x1 x2 x3 x4.(on(e1,x4) & n_obstacle(x4) & a_concrete(s1) & Theme(s1,x4) & Theme(e1,x2) & Actor(e1,x1) & v_do(e1) & n_trick(x2) & of(x2,x3) & n_bicycle(x3) & n_man(x1))
exists e1 x1.(Actor(e1,x1) & v_skateboard(e1) & n_man(x1))