Goal:
    A : Type  B : Type  C : Type  Q : C → Type  P : C → A → Prop
  ============================
   ((∀ x : A, (∀ y : C, Q y → P y x) → B)
    → (∀ l : list A, (∀ y : C, Q y → ∥ All (P y) l ∥) → list B)
      → ∀ (x : A) (xs : list A),
          (∀ y : C, Q y → ∥ All (P y) (x :: xs) ∥)
          → ∀ y : C, Q y → ∥ All (P y) xs ∥)


DEBUG:Going to execute:
let ty := type of B in
           intro || (let H := fresh in
                     intro
                     H)
Level 2: Backtrace:

The first hypothesis in the goal is not an equality.
Level 2: Backtrace:

The first hypothesis in the goal is not an equality.
Level 2: Backtrace:

The first hypothesis in the goal is not an equality.
Level 2: Backtrace:

The first hypothesis in the goal is not an equality.