Goal:
  
  A : Type
  R : ReflectEq A
  x : A
  y : A
  Heq_anonymous : false = (x == y)
  H : x = y
  ============================
   False


DEBUG:Going to execute:
match goal with
           | H':?Y
             |- _ =>
                 match H with
                 | H' => fail 2
                 | _ => unify X Y; clear H' || clear H
                 end
           end
Level 4: Backtrace:

Tactic failure (level 2).
Level 4: Backtrace:

Tactic failure (level 1).
Level 3: Backtrace:

Tactic failure (level 1).
Level 2: Backtrace:

Tactic failure.