Goal:
  
  A : Type
  B : Type
  R : relation A
  S : relation (A * B)
  X : forall (x y : A) (b : B), R x y -> S (x, b) (y, b)
  b : B
  x : A
  ============================
   (clos_refl_trans S (x, b) (x, b))


DEBUG:Going to execute:
econstructor; eauto