(* Will be subsumed by pnatr_eq0 *)

(* Specifications: *)
Lemma divq_num_den x : (numq x)%:Q / (denq x)%:Q = x.
Lemma divq_eq (nx dx ny dy : rat) :
dx != 0 -> dy != 0 -> (nx / dx == ny / dy) = (nx * dy == ny * dx).