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
  a : All_fold (λ (Γ : list A) (d : A), P (n + #|Γ|) d) (x :: List.rev Γ)
  a0 := {| pr1 := x :: List.rev Γ; pr2 := a |}
     : sigma
         (λ index : list A,
            All_fold (λ (Γ : list A) (d : A), P (n + #|Γ|) d) index)
  a1 := x :: List.rev Γ : list A
  a2 := a
     : (λ index : list A,
          All_fold (λ (Γ : list A) (d : A), P (n + #|Γ|) d) index) a1
  ============================
   (let H := CoreTactics.block in
    let H0 := CoreTactics.block in Alli P n (Γ ++ [x]))


DEBUG:Going to execute:
match goal with
           | id'1:=?t:_
             |- _ =>
                 generalize (eq_refl : t = id'1); clearbody id'2 id'1; clear
                  id' id; try unfold signature in id'2; 
                  hnf in id'2; simpl in id'2; rename id'2 into id;
                  cont id id id'1 t
           end
Level 1: Backtrace:

No head constant to reduce.