Theorem blrn

Description: Membership in the range of the ball function. Note that ran ( ballD ) is the collection of all balls for metric D . (Contributed by NM, 31-Aug-2006) (Revised by Mario Carneiro, 12-Nov-2013)

	Ref	Expression
Assertion	blrn	⊢ ( 𝐷 ∈ ( ∞Met ‘ 𝑋 ) → ( 𝐴 ∈ ran ( ball ‘ 𝐷 ) ↔ ∃ 𝑥 ∈ 𝑋 ∃ 𝑟 ∈ ℝ* 𝐴 = ( 𝑥 ( ball ‘ 𝐷 ) 𝑟 ) ) )

Proof

Step	Hyp	Ref	Expression
1		blf	⊢ ( 𝐷 ∈ ( ∞Met ‘ 𝑋 ) → ( ball ‘ 𝐷 ) : ( 𝑋 × ℝ* ) ⟶ 𝒫 𝑋 )
2		ffn	⊢ ( ( ball ‘ 𝐷 ) : ( 𝑋 × ℝ* ) ⟶ 𝒫 𝑋 → ( ball ‘ 𝐷 ) Fn ( 𝑋 × ℝ* ) )
3		ovelrn	⊢ ( ( ball ‘ 𝐷 ) Fn ( 𝑋 × ℝ* ) → ( 𝐴 ∈ ran ( ball ‘ 𝐷 ) ↔ ∃ 𝑥 ∈ 𝑋 ∃ 𝑟 ∈ ℝ* 𝐴 = ( 𝑥 ( ball ‘ 𝐷 ) 𝑟 ) ) )
4	1 2 3	3syl	⊢ ( 𝐷 ∈ ( ∞Met ‘ 𝑋 ) → ( 𝐴 ∈ ran ( ball ‘ 𝐷 ) ↔ ∃ 𝑥 ∈ 𝑋 ∃ 𝑟 ∈ ℝ* 𝐴 = ( 𝑥 ( ball ‘ 𝐷 ) 𝑟 ) ) )