Four boys in water are hanging on to the concrete ledge.
the four boys are swimming
Boys in water are not necessarily swimming. Boys may hang on to the concrete ledge while in water when they are not swimming.
exists e1 s1 x1 x2 x3.(n_ledge(x3) & a_concrete(s1) & Theme(s1,x3) & r_on(e1) & to(e1,x3) & Actor(e1,x1) & v_hang(e1) & in(x1,x2) & n_water(x2) & n_boy(x1) & card_eq_4(x1))
exists e1 x1.(n_boy(x1) & card_eq_4(x1) & Actor(e1,x1) & v_swim(e1))