A cowboy on a horse at a rodeo.
A cowboy is riding a horse at a rodeo.
"cowboy on a horse" is a rephrasing of  "cowboy is riding a horse"
exists x1 x2 x3.(a_topic(x1) & on(x1,x2) & at(x2,x3) & n_rodeo(x3) & n_horse(x2) & n_cowboy(x1))
exists e1 x1 x2 x3.(at(e1,x3) & n_rodeo(x3) & Theme(e1,x2) & Actor(e1,x1) & v_ride(e1) & n_horse(x2) & n_cowboy(x1))