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


DEBUG:Going to execute:
<coq-core.plugins.ltac::econstructor@0>