A person riding a white horse is roping a small animal with horns.
The rodeo cowboy is competing at an event.
A person riding does not imply a rodeo cowboy or competing at an event.
exists e1 e2 s1 s2 x1 x2 x3 x4 x5.(Theme(e2,x4) & Actor(e2,x1) & v_rope(e2) & with(x4,x5) & n_horn(x5) & n_animal(x4) & a_small(s2) & Theme(s2,x4) & Theme(e1,x3) & Actor(e1,x2) & v_ride(e1) & n_horse(x3) & a_white(s1) & Theme(s1,x3) & (x1 = x2) & n_person(x1))
exists e1 x1 x2 x3.(n_cowboy(x1) & of(x1,x2) & n_rodeo(x2) & at(e1,x3) & n_event(x3) & Actor(e1,x1) & v_compete(e1))