Goal:
  
  A : Type
  P : nat → A → Type
  n : nat
  x : A
  Γ : list A
  IHΓ : All_fold (λ (Γ : list A) (d : A), P (n + #|Γ|) d) (List.rev Γ)
        → Alli P n Γ
  ============================
   (All_fold (λ (Γ : list A) (d : A), P (n + #|Γ|) d) (List.rev (Γ ++ [x]))
    → Alli P n (Γ ++ [x]))


DEBUG:Going to execute:
<coq-core.plugins.ssreflect::ssrrewrite@0> $1 $2