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:exists y, _ y |- _ => tac H
           | H:{x : _ | ?P x} |- _ => tac H
           | H:{x : _ & ?P x} |- _ => tacT H
           | H:exists2 x : _, _ x & _ x |- _ => tac2 H
           | H:{x : _ | ?P x & _ x} |- _ => tac2 H
           | H:{x : _ & ?P x & _ x} |- _ => tacT2 H
           end