A stunt plane is billowing smoke into a clear, gray sky.
Someone is writing in the sky.
A stunt plan billowing smoke is not necessarily writing in the sky.
exists e1 s1 s2 s3 x1 x2 x3 x4.(into(e1,x4) & n_sky(x4) & a_gray(s3) & Theme(s3,x4) & a_,(s2) & Theme(s2,x4) & a_clear(s1) & Theme(s1,x4) & Theme(e1,x3) & Actor(e1,x1) & v_billow(e1) & n_smoke(x3) & n_plane(x1) & of(x1,x2) & n_stunt(x2))
exists e1 x1 x2.(n_sky(x2) & in(e1,x2) & Actor(e1,x1) & v_write(e1) & n_person(x1))