Theorems · Theorem · general topology

PseudoMetricSpace.le_two_mul_dist_ofPreNNDist

∀ {X : Type u_1} (d : X → X → NNReal) (dist_self : ∀ (x : X), d x x = 0) (dist_comm : ∀ (x y : X), d x y = d y x),
  (∀ (x₁ x₂ x₃ x₄ : X), d x₁ x₄ ≤ 2 * max (d x₁ x₂) (max (d x₂ x₃) (d x₃ x₄))) → ∀ (x y : X), ↑(d x y) ≤ 2 * dist x y

Consider a function d : X → X → ℝ≥0 such that d x x = 0 and d x y = d y x for all x, y. Let dist be the largest pseudometric distance such that dist x y ≤ d x y, see PseudoMetricSpace.ofPreNNDist. Suppose that d satisfies the following triangle-like inequality: d x₁ x₄ ≤ 2 * max (d x₁ x₂, d x₂ x₃, d x₃ x₄). Then d x y ≤ 2 * dist x y for all x, y.

Defined in

Mathlib.Topology.Metrizable.Uniformity

Cited by

1 results in Mathlib

Foundations

Depth 128 from the axioms · uses propext, Classical.choice, Quot.sound