A polo player cradles a ball while riding a horse.
A polo player is on the field.
In the field always a polo player is on a horse while cradling a ball
exists e2 e1 x1 x2 x3 x4.(while(e1,e2) & Theme(e2,x4) & Actor(e2,x1) & v_ride(e2) & n_horse(x4) & Theme(e1,x3) & Actor(e1,x1) & v_cradle(e1) & n_ball(x3) & n_player(x1) & of(x1,x2) & n_polo(x2))
exists p1 x1 x2 x3.(n_field(x3) & on(x1,x3) & n_player(x1) & of(x1,x2) & n_polo(x2))