One boy skateboarding on a rail and three boys watching.
The boys are all skateboarding
The boys mean more than one boy.
exists e2 e1 x1 x2 x3.(Actor(e2,x3) & v_watch(e2) & n_boy(x3) & card_eq_3(x3) & on(e1,x2) & n_rail(x2) & Actor(e1,x1) & v_skateboard(e1) & n_boy(x1) & card_eq_1(x1))
exists e1 s1 x1.(n_boy(x1) & a_all(s1) & Manner(e1,s1) & Actor(e1,x1) & v_skateboard(e1))