A man in a white helmet crouches while he skateboards.
A man in a white helmet is skateboarding.
A man who skateboards is skateboarding.
(x)
exists e1 s1 x1 x2.(Actor(e1,x1) & v_skateboard(e1) & in(x1,x2) & n_helmet(x2) & a_white(s1) & Theme(s1,x2) & n_man(x1))