A man wakeboarding
the person is skateboarding
A person can not be wakeboarding and skateboarding at the same time.
exists e1 x1 x2.(a_topic(x1) & Actor(e1,x2) & v_wakeboard(e1) & (x1 = x2) & n_man(x1))
exists e1 x1.(n_person(x1) & Actor(e1,x1) & v_skateboard(e1))