proposition: Lemma istriangle_Rabs' : ∏ x y : Reals, (Rabs x - Rabs y <= Rabs (x + y)%R)%NR.
proof: Proof. exact istriangle_hr_abs'. Qed.
imports: UniMath.Algebra.Groups UniMath.Foundations.Preamble UniMath.MoreFoundations.Orders UniMath.MoreFoundations.Tactics UniMath.OrderTheory.Lattice.Lattice UniMath.RealNumbers.Prelim UniMath.RealNumbers.Sets UniMath.RealNumbers.NonnegativeRationals UniMath.RealNumbers.NonnegativeReals