The football players are working on stretching their legs.
The football players are stretching.
"are stretching" is rephrasing of "working on stretching their legs."
exists e1 e2 x1 x2 x3 x4.(n_leg(x4) & of(x4,x1) & n_thing(x1) & n_player(x1) & of(x1,x2) & n_football(x2) & on(e1,e2) & Theme(e2,x4) & Actor(e2,x3) & v_stretch(e2) & Actor(e1,x1) & v_work(e1))
exists e1 x1 x2.(n_player(x1) & of(x1,x2) & n_football(x2) & Actor(e1,x1) & v_stretch(e1))