proposition: Lemma istriangle_Rabs : ∏ x y : Reals, (Rabs (x + y)%R <= Rabs x + Rabs y)%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