a man wearing black rides a unicycle.
A man is doing tricks on a unicycle.
He can't be said to be doing tricks; he is only shown to be riding.
exists x1 x2.(a_topic(x1) & all x3.(n_unicycle(x3) -> exists e1 s1 x4.(Theme(e1,x4) & Actor(e1,x2) & v_wear(e1) & for(x4,x3) & n_ride(x4) & a_black(s1) & Theme(s1,x4))) & (x1 = x2) & n_man(x1))
exists e1 x1 x2 x3.(on(e1,x3) & n_unicycle(x3) & Theme(e1,x2) & Actor(e1,x1) & v_do(e1) & n_trick(x2) & n_man(x1))