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:
cbv beta iota delta [TODO projection TODO projection] in id, id'
DEBUG LTAC Evaluated term: h1
DEBUG LTAC Evaluated term: (list A)
Level 3: type of id
 has value 
(list A)