Goal:
  
  A : Type
  B : Type
  C : Type
  P : A → B → C → Type
  c : C
  b : B
  ls3 : list B
  X0 : All2 (λ (x : A) (y : B), P x y c) [] (b :: ls3)
  X1 : All (λ z : C, All2 (λ (x : A) (y : B), P x y z) [] (b :: ls3)) []
  ============================
   (All2 (λ (x : A) (y : B), All (P x y) [c]) [] (b :: ls3))


DEBUG:Going to execute:
progress subst
Level 0: Backtrace:

Failed to progress.
Level 0: Backtrace:

Failed to progress.