fact: Definition sub (p q : Qp) : option Qp := let 'mk_Qp p Hp := p in let 'mk_Qp q Hq := q in let pq := (p - q)%Qc in Hpq ← guard (0 < pq)%Qc; Some (mk_Qp pq Hpq).
imports: Coq(QArith Qcanon) stdpp(well_founded) stdpp(options)