Goal:
  
  A : Type
  P : A → A → Type
  Q : A → Type
  HPQ : ∀ x y : A, Q x → P x y → Q y
  hd : A
  hd' : A
  tl : list A
  p : P hd hd'
  x : A
  l : list A
  q : Q x
  H : All Q l
  ============================
   (hd :: tl = x :: l
    → let H := CoreTactics.block in
      let H0 := CoreTactics.block in All Q (hd' :: tl))


DEBUG:Going to execute:
DepElim.simplify_one_dep_elim