Metamath Proof Explorer


Theorem blnei

Description: A ball around a point is a neighborhood of the point. (Contributed by NM, 8-Nov-2007) (Revised by Mario Carneiro, 24-Aug-2015)

Ref Expression
Hypothesis mopni.1 ⊒ 𝐽 = ( MetOpen β€˜ 𝐷 )
Assertion blnei ( ( 𝐷 ∈ ( ∞Met β€˜ 𝑋 ) ∧ 𝑃 ∈ 𝑋 ∧ 𝑅 ∈ ℝ+ ) β†’ ( 𝑃 ( ball β€˜ 𝐷 ) 𝑅 ) ∈ ( ( nei β€˜ 𝐽 ) β€˜ { 𝑃 } ) )

Proof

Step Hyp Ref Expression
1 mopni.1 ⊒ 𝐽 = ( MetOpen β€˜ 𝐷 )
2 1 mopntop ⊒ ( 𝐷 ∈ ( ∞Met β€˜ 𝑋 ) β†’ 𝐽 ∈ Top )
3 2 3ad2ant1 ⊒ ( ( 𝐷 ∈ ( ∞Met β€˜ 𝑋 ) ∧ 𝑃 ∈ 𝑋 ∧ 𝑅 ∈ ℝ+ ) β†’ 𝐽 ∈ Top )
4 rpxr ⊒ ( 𝑅 ∈ ℝ+ β†’ 𝑅 ∈ ℝ* )
5 1 blopn ⊒ ( ( 𝐷 ∈ ( ∞Met β€˜ 𝑋 ) ∧ 𝑃 ∈ 𝑋 ∧ 𝑅 ∈ ℝ* ) β†’ ( 𝑃 ( ball β€˜ 𝐷 ) 𝑅 ) ∈ 𝐽 )
6 4 5 syl3an3 ⊒ ( ( 𝐷 ∈ ( ∞Met β€˜ 𝑋 ) ∧ 𝑃 ∈ 𝑋 ∧ 𝑅 ∈ ℝ+ ) β†’ ( 𝑃 ( ball β€˜ 𝐷 ) 𝑅 ) ∈ 𝐽 )
7 blcntr ⊒ ( ( 𝐷 ∈ ( ∞Met β€˜ 𝑋 ) ∧ 𝑃 ∈ 𝑋 ∧ 𝑅 ∈ ℝ+ ) β†’ 𝑃 ∈ ( 𝑃 ( ball β€˜ 𝐷 ) 𝑅 ) )
8 opnneip ⊒ ( ( 𝐽 ∈ Top ∧ ( 𝑃 ( ball β€˜ 𝐷 ) 𝑅 ) ∈ 𝐽 ∧ 𝑃 ∈ ( 𝑃 ( ball β€˜ 𝐷 ) 𝑅 ) ) β†’ ( 𝑃 ( ball β€˜ 𝐷 ) 𝑅 ) ∈ ( ( nei β€˜ 𝐽 ) β€˜ { 𝑃 } ) )
9 3 6 7 8 syl3anc ⊒ ( ( 𝐷 ∈ ( ∞Met β€˜ 𝑋 ) ∧ 𝑃 ∈ 𝑋 ∧ 𝑅 ∈ ℝ+ ) β†’ ( 𝑃 ( ball β€˜ 𝐷 ) 𝑅 ) ∈ ( ( nei β€˜ 𝐽 ) β€˜ { 𝑃 } ) )