People are stretching on yoga mats.
They stretched on yoga mats outside.
People can stretch on yoga mats in places other than outside as well.
exists e1 x1 x2 x3.(on(e1,x2) & n_mat(x2) & of(x2,x3) & n_yoga(x3) & Actor(e1,x1) & v_stretch(e1) & n_people(x1))
exists e1 s1 x1 x2.(a_outside(s1) & Manner(e1,s1) & on(e1,x1) & n_mat(x1) & of(x1,x2) & n_yoga(x2) & Actor(e1,x1) & v_stretch(e1) & n_thing(x1))