Goal:
    x : t  y : t  Heq_anonymous : false = eqb 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