Metamath Proof Explorer


Theorem blbas

Description: The balls of a metric space form a basis for a topology. (Contributed by NM, 12-Sep-2006) (Revised by Mario Carneiro, 15-Jan-2014)

Ref Expression
Assertion blbas ( 𝐷 ∈ ( ∞Met β€˜ 𝑋 ) β†’ ran ( ball β€˜ 𝐷 ) ∈ TopBases )

Proof

Step Hyp Ref Expression
1 blin2 ⊒ ( ( ( 𝐷 ∈ ( ∞Met β€˜ 𝑋 ) ∧ 𝑧 ∈ ( π‘₯ ∩ 𝑦 ) ) ∧ ( π‘₯ ∈ ran ( ball β€˜ 𝐷 ) ∧ 𝑦 ∈ ran ( ball β€˜ 𝐷 ) ) ) β†’ βˆƒ π‘Ÿ ∈ ℝ+ ( 𝑧 ( ball β€˜ 𝐷 ) π‘Ÿ ) βŠ† ( π‘₯ ∩ 𝑦 ) )
2 simpll ⊒ ( ( ( 𝐷 ∈ ( ∞Met β€˜ 𝑋 ) ∧ 𝑧 ∈ ( π‘₯ ∩ 𝑦 ) ) ∧ ( π‘₯ ∈ ran ( ball β€˜ 𝐷 ) ∧ 𝑦 ∈ ran ( ball β€˜ 𝐷 ) ) ) β†’ 𝐷 ∈ ( ∞Met β€˜ 𝑋 ) )
3 elinel1 ⊒ ( 𝑧 ∈ ( π‘₯ ∩ 𝑦 ) β†’ 𝑧 ∈ π‘₯ )
4 elunii ⊒ ( ( 𝑧 ∈ π‘₯ ∧ π‘₯ ∈ ran ( ball β€˜ 𝐷 ) ) β†’ 𝑧 ∈ βˆͺ ran ( ball β€˜ 𝐷 ) )
5 3 4 sylan ⊒ ( ( 𝑧 ∈ ( π‘₯ ∩ 𝑦 ) ∧ π‘₯ ∈ ran ( ball β€˜ 𝐷 ) ) β†’ 𝑧 ∈ βˆͺ ran ( ball β€˜ 𝐷 ) )
6 5 ad2ant2lr ⊒ ( ( ( 𝐷 ∈ ( ∞Met β€˜ 𝑋 ) ∧ 𝑧 ∈ ( π‘₯ ∩ 𝑦 ) ) ∧ ( π‘₯ ∈ ran ( ball β€˜ 𝐷 ) ∧ 𝑦 ∈ ran ( ball β€˜ 𝐷 ) ) ) β†’ 𝑧 ∈ βˆͺ ran ( ball β€˜ 𝐷 ) )
7 unirnbl ⊒ ( 𝐷 ∈ ( ∞Met β€˜ 𝑋 ) β†’ βˆͺ ran ( ball β€˜ 𝐷 ) = 𝑋 )
8 7 ad2antrr ⊒ ( ( ( 𝐷 ∈ ( ∞Met β€˜ 𝑋 ) ∧ 𝑧 ∈ ( π‘₯ ∩ 𝑦 ) ) ∧ ( π‘₯ ∈ ran ( ball β€˜ 𝐷 ) ∧ 𝑦 ∈ ran ( ball β€˜ 𝐷 ) ) ) β†’ βˆͺ ran ( ball β€˜ 𝐷 ) = 𝑋 )
9 6 8 eleqtrd ⊒ ( ( ( 𝐷 ∈ ( ∞Met β€˜ 𝑋 ) ∧ 𝑧 ∈ ( π‘₯ ∩ 𝑦 ) ) ∧ ( π‘₯ ∈ ran ( ball β€˜ 𝐷 ) ∧ 𝑦 ∈ ran ( ball β€˜ 𝐷 ) ) ) β†’ 𝑧 ∈ 𝑋 )
10 blssex ⊒ ( ( 𝐷 ∈ ( ∞Met β€˜ 𝑋 ) ∧ 𝑧 ∈ 𝑋 ) β†’ ( βˆƒ 𝑏 ∈ ran ( ball β€˜ 𝐷 ) ( 𝑧 ∈ 𝑏 ∧ 𝑏 βŠ† ( π‘₯ ∩ 𝑦 ) ) ↔ βˆƒ π‘Ÿ ∈ ℝ+ ( 𝑧 ( ball β€˜ 𝐷 ) π‘Ÿ ) βŠ† ( π‘₯ ∩ 𝑦 ) ) )
11 2 9 10 syl2anc ⊒ ( ( ( 𝐷 ∈ ( ∞Met β€˜ 𝑋 ) ∧ 𝑧 ∈ ( π‘₯ ∩ 𝑦 ) ) ∧ ( π‘₯ ∈ ran ( ball β€˜ 𝐷 ) ∧ 𝑦 ∈ ran ( ball β€˜ 𝐷 ) ) ) β†’ ( βˆƒ 𝑏 ∈ ran ( ball β€˜ 𝐷 ) ( 𝑧 ∈ 𝑏 ∧ 𝑏 βŠ† ( π‘₯ ∩ 𝑦 ) ) ↔ βˆƒ π‘Ÿ ∈ ℝ+ ( 𝑧 ( ball β€˜ 𝐷 ) π‘Ÿ ) βŠ† ( π‘₯ ∩ 𝑦 ) ) )
12 1 11 mpbird ⊒ ( ( ( 𝐷 ∈ ( ∞Met β€˜ 𝑋 ) ∧ 𝑧 ∈ ( π‘₯ ∩ 𝑦 ) ) ∧ ( π‘₯ ∈ ran ( ball β€˜ 𝐷 ) ∧ 𝑦 ∈ ran ( ball β€˜ 𝐷 ) ) ) β†’ βˆƒ 𝑏 ∈ ran ( ball β€˜ 𝐷 ) ( 𝑧 ∈ 𝑏 ∧ 𝑏 βŠ† ( π‘₯ ∩ 𝑦 ) ) )
13 12 ex ⊒ ( ( 𝐷 ∈ ( ∞Met β€˜ 𝑋 ) ∧ 𝑧 ∈ ( π‘₯ ∩ 𝑦 ) ) β†’ ( ( π‘₯ ∈ ran ( ball β€˜ 𝐷 ) ∧ 𝑦 ∈ ran ( ball β€˜ 𝐷 ) ) β†’ βˆƒ 𝑏 ∈ ran ( ball β€˜ 𝐷 ) ( 𝑧 ∈ 𝑏 ∧ 𝑏 βŠ† ( π‘₯ ∩ 𝑦 ) ) ) )
14 13 ralrimdva ⊒ ( 𝐷 ∈ ( ∞Met β€˜ 𝑋 ) β†’ ( ( π‘₯ ∈ ran ( ball β€˜ 𝐷 ) ∧ 𝑦 ∈ ran ( ball β€˜ 𝐷 ) ) β†’ βˆ€ 𝑧 ∈ ( π‘₯ ∩ 𝑦 ) βˆƒ 𝑏 ∈ ran ( ball β€˜ 𝐷 ) ( 𝑧 ∈ 𝑏 ∧ 𝑏 βŠ† ( π‘₯ ∩ 𝑦 ) ) ) )
15 14 ralrimivv ⊒ ( 𝐷 ∈ ( ∞Met β€˜ 𝑋 ) β†’ βˆ€ π‘₯ ∈ ran ( ball β€˜ 𝐷 ) βˆ€ 𝑦 ∈ ran ( ball β€˜ 𝐷 ) βˆ€ 𝑧 ∈ ( π‘₯ ∩ 𝑦 ) βˆƒ 𝑏 ∈ ran ( ball β€˜ 𝐷 ) ( 𝑧 ∈ 𝑏 ∧ 𝑏 βŠ† ( π‘₯ ∩ 𝑦 ) ) )
16 fvex ⊒ ( ball β€˜ 𝐷 ) ∈ V
17 16 rnex ⊒ ran ( ball β€˜ 𝐷 ) ∈ V
18 isbasis2g ⊒ ( ran ( ball β€˜ 𝐷 ) ∈ V β†’ ( ran ( ball β€˜ 𝐷 ) ∈ TopBases ↔ βˆ€ π‘₯ ∈ ran ( ball β€˜ 𝐷 ) βˆ€ 𝑦 ∈ ran ( ball β€˜ 𝐷 ) βˆ€ 𝑧 ∈ ( π‘₯ ∩ 𝑦 ) βˆƒ 𝑏 ∈ ran ( ball β€˜ 𝐷 ) ( 𝑧 ∈ 𝑏 ∧ 𝑏 βŠ† ( π‘₯ ∩ 𝑦 ) ) ) )
19 17 18 ax-mp ⊒ ( ran ( ball β€˜ 𝐷 ) ∈ TopBases ↔ βˆ€ π‘₯ ∈ ran ( ball β€˜ 𝐷 ) βˆ€ 𝑦 ∈ ran ( ball β€˜ 𝐷 ) βˆ€ 𝑧 ∈ ( π‘₯ ∩ 𝑦 ) βˆƒ 𝑏 ∈ ran ( ball β€˜ 𝐷 ) ( 𝑧 ∈ 𝑏 ∧ 𝑏 βŠ† ( π‘₯ ∩ 𝑦 ) ) )
20 15 19 sylibr ⊒ ( 𝐷 ∈ ( ∞Met β€˜ 𝑋 ) β†’ ran ( ball β€˜ 𝐷 ) ∈ TopBases )