A rodeo cowboy is riding a rambunctious horse.
The cowboy is riding the unbroke horse for the first time.
All rambunctious horses are not necessarily 'unbroke' and there just because the horse is rambunctious does not mean that it's the first time the cowboy has ridden it or that the horse hasn't been ridden.
exists e1 s1 x1 x2 x3.(Theme(e1,x3) & Actor(e1,x1) & v_ride(e1) & n_horse(x3) & a_rambunctious(s1) & Theme(s1,x3) & n_cowboy(x1) & of(x1,x2) & n_rodeo(x2))
exists e1 s1 s2 x1 x2 x3.(n_time(x3) & a_first(s2) & Theme(s2,x3) & n_horse(x2) & a_unbroke(s1) & Theme(s1,x2) & n_cowboy(x1) & for(e1,x3) & Theme(e1,x2) & Actor(e1,x1) & v_ride(e1))