A man is riding a bicycle.
A man is on a unicycle
A bicycle is different from a unicycle.
exists e1 x1 x2.(Theme(e1,x2) & Actor(e1,x1) & v_ride(e1) & n_bicycle(x2) & n_man(x1))
exists p1 x1.(exists x2.(on(x1,x2) & n_unicycle(x2)) & n_man(x1))