They swim laps across the pool.
The boys are swimming in the pool.
swim is another form of swimming
exists e1 x1 x2 x3.(n_pool(x3) & n_thing(x1) & Theme(e1,x2) & Actor(e1,x1) & v_swim(e1) & across(x2,x3) & n_lap(x2))
exists e1 x1 x2.(n_pool(x2) & n_boy(x1) & in(e1,x2) & Actor(e1,x1) & v_swim(e1))