Goal:
  
  A : Type
  B : Type
  C : Type
  Q : C → Type
  P : C → A → Prop
  x : A
  xs : list A
  y : C
  X : Q y
  h1 : list A
  h : All (P y) h1
  ============================
   (x :: xs = h1
    → let H := CoreTactics.block in
      let H0 := CoreTactics.block in All (P y) xs)


DEBUG:Going to execute:
first
[ match p with
  | _ => generalize dependent p; intros p
  end
| intros
until
p
| intros
until
1
| intros ]