-(* Inversion lemmas with pushs **********************************************)
-
-lemma coafter_fwd_pushs: ∀n,g2,g1,g. g2 ~⊚ g1 ≡ g → @⦃0, g2⦄ ≡ n →
- ∃f. ↑*[n]f = g.
-#n elim n -n /2 width=2 by ex_intro/
-#n #IH #g2 #g1 #g #Hg #Hg2
-cases (at_inv_pxn … Hg2) -Hg2 [ |*: // ] #f2 #Hf2 #H2
-cases (coafter_inv_nxx … Hg … H2) -Hg -H2 #f #Hf #H0 destruct
-elim (IH … Hf Hf2) -g1 -g2 -f2 /2 width=2 by ex_intro/
+(* Forward lemmas with pushs ************************************************)
+
+lemma coafter_fwd_pushs: ∀j,i,g2,f1,g. g2 ~⊚ ↑*[i]f1 ≡ g → @⦃i, g2⦄ ≡ j →
+ ∃f. ↑*[j] f = g.
+#j elim j -j
+[ #i #g2 #f1 #g #Hg #H
+ elim (at_inv_xxp … H) -H [|*: // ] #f2 #H1 #H2 destruct
+ /2 width=2 by ex_intro/
+| #j #IH * [| #i ] #g2 #f1 #g #Hg #H
+ [ elim (at_inv_pxn … H) -H [|*: // ] #f2 #Hij #H destruct
+ elim (coafter_inv_nxx … Hg) -Hg [|*: // ] #f #Hf #H destruct
+ elim (IH … Hf Hij) -f1 -f2 -IH /2 width=2 by ex_intro/
+ | elim (at_inv_nxn … H) -H [1,4: * |*: // ] #f2 #Hij #H destruct
+ [ elim (coafter_inv_ppx … Hg) -Hg [|*: // ] #f #Hf #H destruct
+ elim (IH … Hf Hij) -f1 -f2 -i /2 width=2 by ex_intro/
+ | elim (coafter_inv_nxx … Hg) -Hg [|*: // ] #f #Hf #H destruct
+ elim (IH … Hf Hij) -f1 -f2 -i /2 width=2 by ex_intro/
+ ]
+ ]
+]