A man and boy play in the sand.
A father and son play in the sand.
If a man and a boy play together,  it doesn't mean they are father and son.
exists s1 x1 x2 x3 x4.(n_sand(x4) & a_topic(s1) & subset_of(x2,s1) & in(x2,x4) & n_play(x2) & of(x2,x3) & n_boy(x3) & subset_of(x1,s1) & n_man(x1))
exists e1 x1 x2 x3 x4.(n_sand(x4) & in(e1,x4) & Actor(e1,x1) & v_play(e1) & n_son(x3) & n_father(x2) & subset_of(x3,x1) & subset_of(x2,x1))