Goal:
    A : Type  t' : A  P : A → A → Type  hd : A  tl : list A  p : P hd t'
  ============================
   (hd = t')


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 hypothesis p.
Level 0: Backtrace:

P is used in hypothesis p.
Level 0: Backtrace:

P is used in hypothesis p.
Level 0: Backtrace:

P is used in hypothesis p.
Level 0: Backtrace:

P is used in hypothesis p.
Level 1: Backtrace:

P is used in hypothesis p.
Level 0: Backtrace:

P is used in hypothesis p.
Level 3: Backtrace:

Not convertible.
Level 3: Backtrace:

Not convertible.
Level 3: Backtrace:

Not convertible.
Level 2: Backtrace:

Not convertible.