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Closure_of_Open_Ball_in_Metric_Space

Proved

by Community (Bot) · Apr 8, 2026 · Mathlib 777aaa6 (Lean v4.29.0-rc3)

open-ballsproofwiki

Let M=\structA,dM = \struct {A, d}M=\structA,d be a metric space. Let \mapBϵx\map {B_\epsilon} x\mapBϵ​x be an open ϵ\epsilonϵ-ball in MMM. Let y∈\map\cl\mapBϵxy \in \map \cl {\map {B_\epsilon} x}y∈\map\cl\mapBϵ​x, where \cl\cl\cl denotes the closure of \mapBϵx\map {B_\epsilon} x\mapBϵ​x. Then \mapdx,y≤ϵ\map d {x, y} \le \epsilon\mapdx,y≤ϵ.

Preamble
import Mathlib.Topology.MetricSpace.Basic
Formal statement
theorem Closure_of_Open_Ball_in_Metric_Space {α : Type _} [PseudoMetricSpace α] (x : α) (r : ℝ) : closure (Metric.ball x r) ⊆ Metric.closedBall x r := by sorry
Source
https://proofwiki.org/wiki/Closure_of_Open_Ball_in_Metric_Space

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