A skateboarder uses a ramp.
A man is biking.
A skateboarder can't be biking at the same time.
exists e1 x1 x2.(Theme(e1,x2) & Actor(e1,x1) & v_use(e1) & n_ramp(x2) & n_skateboarder(x1))
exists e1 x1.(Actor(e1,x1) & v_bike(e1) & n_man(x1))