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


DEBUG:Going to execute:
fun tac => match goal with
                      | H:?f ?a = ?f' ?a' |- _ => tac H
                      end