Goal:
  
  A : Type
  P : A → A → Type
  r : A
  r' : A
  X : All2 P [r] ([] ++ [r'])
  x : A
  y : A
  l : list A
  l' : list A
  X0 : P r r'
  X1 : All2 P [] []
  H0 : x = r
  H1 : l = []
  H : y = r'
  H3 : l' = []
  ============================
   (All2 P [] [] × P r r')


DEBUG:Going to execute:
<Coq.Init.Tauto.is_unit_or_eq> flags X1; Ltac.cut X2;
            [ intro; clear id
            | Ltac.cut X1; [ exact id | constructor 1; fail ] ]
Level 0: Backtrace:

P is used in conclusion.
Level 0: Backtrace:

P is used in conclusion.
Level 0: Backtrace:

P is used in conclusion.
Level 0: Backtrace:

P is used in conclusion.
Level 0: Backtrace:

P is used in conclusion.
Level 1: Backtrace:

P is used in conclusion.
Level 0: Backtrace:

P is used in conclusion.
Level 2: Backtrace:

Not convertible.
Level 2: Backtrace:

Not convertible.
Level 2: Backtrace:

Not convertible.
Level 1: Backtrace:

Not convertible.