A man wearing a gray shirt is playing guitar.
Nobody has a shirt.
A man wearing a gray shirt is different than nobody having a shirt
exists e1 e2 s1 x1 x2 x3 x4.(Theme(e2,x4) & Actor(e2,x1) & v_play(e2) & n_guitar(x4) & Theme(e1,x3) & Actor(e1,x2) & v_wear(e1) & n_shirt(x3) & a_gray(s1) & Theme(s1,x3) & (x1 = x2) & n_man(x1))
-exists e1 x1 x2.(Theme(e1,x2) & Actor(e1,x1) & v_have(e1) & n_shirt(x2) & n_person(x1))