a boy smiles underwater.
A boy is trying to catch a fish underwater.
Just because, the boy is underwater does not mean the boy is trying to catch a fish.
exists e1 x1 x2.(Theme(e1,x2) & Actor(e1,x1) & v_smile(e1) & n_underwater(x2) & n_boy(x1))
exists e1 p1 x1.(Topic(e1,p1) & Actor(e1,x1) & v_try(e1) & exists e2 x2 x3.(Theme(e2,x2) & Actor(e2,x1) & v_catch(e2) & n_underwater(x2) & of(x2,x3) & n_fish(x3)) & n_boy(x1))