a man walks across the tightrope.
an acrobat walks acros a tightrope
A man does not have to be an acrobat to walks across a tightrope.
exists e1 x1 x2.(n_tightrope(x2) & across(e1,x2) & Actor(e1,x1) & v_walk(e1) & n_man(x1))
exists x1.(all x2.(n_tightrope(x2) -> exists e1 x3.(Theme(e1,x3) & Actor(e1,x1) & v_walk(e1) & for(x3,x2) & n_acro(x3))) & n_acrobat(x1))