#f21 #f1 #f #g21 [1,2: #g1 ] #g #Hf #H21 [1,2: #H1 ] #H #g22 #H0
[ cases (eq_inv_px … H0 … H21) -g21 /3 width=7 by after_refl/
| cases (eq_inv_px … H0 … H21) -g21 /3 width=7 by after_push/
#f21 #f1 #f #g21 [1,2: #g1 ] #g #Hf #H21 [1,2: #H1 ] #H #g22 #H0
[ cases (eq_inv_px … H0 … H21) -g21 /3 width=7 by after_refl/
| cases (eq_inv_px … H0 … H21) -g21 /3 width=7 by after_push/