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Description: Express the binary relation "sequence F converges to point P " in a metric space. Definition 1.4-1 of Kreyszig p. 25. The condition F C_ ( CC X. X ) allows to use objects more general than sequences when convenient; see the comment in df-lm . (Contributed by NM, 7-Dec-2006) (Revised by Mario Carneiro, 1-May-2014)
| Ref | Expression | ||
|---|---|---|---|
| Hypotheses | lmmbr.2 | ⊢ 𝐽 = ( MetOpen ‘ 𝐷 ) | |
| lmmbr.3 | ⊢ ( 𝜑 → 𝐷 ∈ ( ∞Met ‘ 𝑋 ) ) | ||
| Assertion | lmmbr | ⊢ ( 𝜑 → ( 𝐹 ( ⇝𝑡 ‘ 𝐽 ) 𝑃 ↔ ( 𝐹 ∈ ( 𝑋 ↑pm ℂ ) ∧ 𝑃 ∈ 𝑋 ∧ ∀ 𝑥 ∈ ℝ+ ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) ) ) ) |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | lmmbr.2 | ⊢ 𝐽 = ( MetOpen ‘ 𝐷 ) | |
| 2 | lmmbr.3 | ⊢ ( 𝜑 → 𝐷 ∈ ( ∞Met ‘ 𝑋 ) ) | |
| 3 | 1 | mopntopon | ⊢ ( 𝐷 ∈ ( ∞Met ‘ 𝑋 ) → 𝐽 ∈ ( TopOn ‘ 𝑋 ) ) |
| 4 | 2 3 | syl | ⊢ ( 𝜑 → 𝐽 ∈ ( TopOn ‘ 𝑋 ) ) |
| 5 | 4 | lmbr | ⊢ ( 𝜑 → ( 𝐹 ( ⇝𝑡 ‘ 𝐽 ) 𝑃 ↔ ( 𝐹 ∈ ( 𝑋 ↑pm ℂ ) ∧ 𝑃 ∈ 𝑋 ∧ ∀ 𝑢 ∈ 𝐽 ( 𝑃 ∈ 𝑢 → ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ 𝑢 ) ) ) ) |
| 6 | rpxr | ⊢ ( 𝑥 ∈ ℝ+ → 𝑥 ∈ ℝ* ) | |
| 7 | 1 | blopn | ⊢ ( ( 𝐷 ∈ ( ∞Met ‘ 𝑋 ) ∧ 𝑃 ∈ 𝑋 ∧ 𝑥 ∈ ℝ* ) → ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) ∈ 𝐽 ) |
| 8 | 6 7 | syl3an3 | ⊢ ( ( 𝐷 ∈ ( ∞Met ‘ 𝑋 ) ∧ 𝑃 ∈ 𝑋 ∧ 𝑥 ∈ ℝ+ ) → ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) ∈ 𝐽 ) |
| 9 | blcntr | ⊢ ( ( 𝐷 ∈ ( ∞Met ‘ 𝑋 ) ∧ 𝑃 ∈ 𝑋 ∧ 𝑥 ∈ ℝ+ ) → 𝑃 ∈ ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) ) | |
| 10 | eleq2 | ⊢ ( 𝑢 = ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) → ( 𝑃 ∈ 𝑢 ↔ 𝑃 ∈ ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) ) ) | |
| 11 | feq3 | ⊢ ( 𝑢 = ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) → ( ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ 𝑢 ↔ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) ) ) | |
| 12 | 11 | rexbidv | ⊢ ( 𝑢 = ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) → ( ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ 𝑢 ↔ ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) ) ) |
| 13 | 10 12 | imbi12d | ⊢ ( 𝑢 = ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) → ( ( 𝑃 ∈ 𝑢 → ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ 𝑢 ) ↔ ( 𝑃 ∈ ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) → ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) ) ) ) |
| 14 | 13 | rspcva | ⊢ ( ( ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) ∈ 𝐽 ∧ ∀ 𝑢 ∈ 𝐽 ( 𝑃 ∈ 𝑢 → ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ 𝑢 ) ) → ( 𝑃 ∈ ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) → ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) ) ) |
| 15 | 14 | impancom | ⊢ ( ( ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) ∈ 𝐽 ∧ 𝑃 ∈ ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) ) → ( ∀ 𝑢 ∈ 𝐽 ( 𝑃 ∈ 𝑢 → ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ 𝑢 ) → ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) ) ) |
| 16 | 8 9 15 | syl2anc | ⊢ ( ( 𝐷 ∈ ( ∞Met ‘ 𝑋 ) ∧ 𝑃 ∈ 𝑋 ∧ 𝑥 ∈ ℝ+ ) → ( ∀ 𝑢 ∈ 𝐽 ( 𝑃 ∈ 𝑢 → ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ 𝑢 ) → ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) ) ) |
| 17 | 16 | 3expa | ⊢ ( ( ( 𝐷 ∈ ( ∞Met ‘ 𝑋 ) ∧ 𝑃 ∈ 𝑋 ) ∧ 𝑥 ∈ ℝ+ ) → ( ∀ 𝑢 ∈ 𝐽 ( 𝑃 ∈ 𝑢 → ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ 𝑢 ) → ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) ) ) |
| 18 | 17 | adantlrl | ⊢ ( ( ( 𝐷 ∈ ( ∞Met ‘ 𝑋 ) ∧ ( 𝐹 ∈ ( 𝑋 ↑pm ℂ ) ∧ 𝑃 ∈ 𝑋 ) ) ∧ 𝑥 ∈ ℝ+ ) → ( ∀ 𝑢 ∈ 𝐽 ( 𝑃 ∈ 𝑢 → ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ 𝑢 ) → ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) ) ) |
| 19 | 18 | impancom | ⊢ ( ( ( 𝐷 ∈ ( ∞Met ‘ 𝑋 ) ∧ ( 𝐹 ∈ ( 𝑋 ↑pm ℂ ) ∧ 𝑃 ∈ 𝑋 ) ) ∧ ∀ 𝑢 ∈ 𝐽 ( 𝑃 ∈ 𝑢 → ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ 𝑢 ) ) → ( 𝑥 ∈ ℝ+ → ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) ) ) |
| 20 | 19 | ralrimiv | ⊢ ( ( ( 𝐷 ∈ ( ∞Met ‘ 𝑋 ) ∧ ( 𝐹 ∈ ( 𝑋 ↑pm ℂ ) ∧ 𝑃 ∈ 𝑋 ) ) ∧ ∀ 𝑢 ∈ 𝐽 ( 𝑃 ∈ 𝑢 → ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ 𝑢 ) ) → ∀ 𝑥 ∈ ℝ+ ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) ) |
| 21 | 1 | mopni2 | ⊢ ( ( 𝐷 ∈ ( ∞Met ‘ 𝑋 ) ∧ 𝑢 ∈ 𝐽 ∧ 𝑃 ∈ 𝑢 ) → ∃ 𝑥 ∈ ℝ+ ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) ⊆ 𝑢 ) |
| 22 | r19.29 | ⊢ ( ( ∀ 𝑥 ∈ ℝ+ ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) ∧ ∃ 𝑥 ∈ ℝ+ ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) ⊆ 𝑢 ) → ∃ 𝑥 ∈ ℝ+ ( ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) ∧ ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) ⊆ 𝑢 ) ) | |
| 23 | fss | ⊢ ( ( ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) ∧ ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) ⊆ 𝑢 ) → ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ 𝑢 ) | |
| 24 | 23 | expcom | ⊢ ( ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) ⊆ 𝑢 → ( ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) → ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ 𝑢 ) ) |
| 25 | 24 | reximdv | ⊢ ( ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) ⊆ 𝑢 → ( ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) → ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ 𝑢 ) ) |
| 26 | 25 | impcom | ⊢ ( ( ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) ∧ ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) ⊆ 𝑢 ) → ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ 𝑢 ) |
| 27 | 26 | rexlimivw | ⊢ ( ∃ 𝑥 ∈ ℝ+ ( ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) ∧ ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) ⊆ 𝑢 ) → ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ 𝑢 ) |
| 28 | 22 27 | syl | ⊢ ( ( ∀ 𝑥 ∈ ℝ+ ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) ∧ ∃ 𝑥 ∈ ℝ+ ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) ⊆ 𝑢 ) → ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ 𝑢 ) |
| 29 | 21 28 | sylan2 | ⊢ ( ( ∀ 𝑥 ∈ ℝ+ ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) ∧ ( 𝐷 ∈ ( ∞Met ‘ 𝑋 ) ∧ 𝑢 ∈ 𝐽 ∧ 𝑃 ∈ 𝑢 ) ) → ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ 𝑢 ) |
| 30 | 29 | 3exp2 | ⊢ ( ∀ 𝑥 ∈ ℝ+ ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) → ( 𝐷 ∈ ( ∞Met ‘ 𝑋 ) → ( 𝑢 ∈ 𝐽 → ( 𝑃 ∈ 𝑢 → ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ 𝑢 ) ) ) ) |
| 31 | 30 | impcom | ⊢ ( ( 𝐷 ∈ ( ∞Met ‘ 𝑋 ) ∧ ∀ 𝑥 ∈ ℝ+ ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) ) → ( 𝑢 ∈ 𝐽 → ( 𝑃 ∈ 𝑢 → ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ 𝑢 ) ) ) |
| 32 | 31 | adantlr | ⊢ ( ( ( 𝐷 ∈ ( ∞Met ‘ 𝑋 ) ∧ ( 𝐹 ∈ ( 𝑋 ↑pm ℂ ) ∧ 𝑃 ∈ 𝑋 ) ) ∧ ∀ 𝑥 ∈ ℝ+ ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) ) → ( 𝑢 ∈ 𝐽 → ( 𝑃 ∈ 𝑢 → ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ 𝑢 ) ) ) |
| 33 | 32 | ralrimiv | ⊢ ( ( ( 𝐷 ∈ ( ∞Met ‘ 𝑋 ) ∧ ( 𝐹 ∈ ( 𝑋 ↑pm ℂ ) ∧ 𝑃 ∈ 𝑋 ) ) ∧ ∀ 𝑥 ∈ ℝ+ ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) ) → ∀ 𝑢 ∈ 𝐽 ( 𝑃 ∈ 𝑢 → ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ 𝑢 ) ) |
| 34 | 20 33 | impbida | ⊢ ( ( 𝐷 ∈ ( ∞Met ‘ 𝑋 ) ∧ ( 𝐹 ∈ ( 𝑋 ↑pm ℂ ) ∧ 𝑃 ∈ 𝑋 ) ) → ( ∀ 𝑢 ∈ 𝐽 ( 𝑃 ∈ 𝑢 → ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ 𝑢 ) ↔ ∀ 𝑥 ∈ ℝ+ ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) ) ) |
| 35 | 34 | pm5.32da | ⊢ ( 𝐷 ∈ ( ∞Met ‘ 𝑋 ) → ( ( ( 𝐹 ∈ ( 𝑋 ↑pm ℂ ) ∧ 𝑃 ∈ 𝑋 ) ∧ ∀ 𝑢 ∈ 𝐽 ( 𝑃 ∈ 𝑢 → ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ 𝑢 ) ) ↔ ( ( 𝐹 ∈ ( 𝑋 ↑pm ℂ ) ∧ 𝑃 ∈ 𝑋 ) ∧ ∀ 𝑥 ∈ ℝ+ ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) ) ) ) |
| 36 | df-3an | ⊢ ( ( 𝐹 ∈ ( 𝑋 ↑pm ℂ ) ∧ 𝑃 ∈ 𝑋 ∧ ∀ 𝑢 ∈ 𝐽 ( 𝑃 ∈ 𝑢 → ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ 𝑢 ) ) ↔ ( ( 𝐹 ∈ ( 𝑋 ↑pm ℂ ) ∧ 𝑃 ∈ 𝑋 ) ∧ ∀ 𝑢 ∈ 𝐽 ( 𝑃 ∈ 𝑢 → ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ 𝑢 ) ) ) | |
| 37 | df-3an | ⊢ ( ( 𝐹 ∈ ( 𝑋 ↑pm ℂ ) ∧ 𝑃 ∈ 𝑋 ∧ ∀ 𝑥 ∈ ℝ+ ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) ) ↔ ( ( 𝐹 ∈ ( 𝑋 ↑pm ℂ ) ∧ 𝑃 ∈ 𝑋 ) ∧ ∀ 𝑥 ∈ ℝ+ ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) ) ) | |
| 38 | 35 36 37 | 3bitr4g | ⊢ ( 𝐷 ∈ ( ∞Met ‘ 𝑋 ) → ( ( 𝐹 ∈ ( 𝑋 ↑pm ℂ ) ∧ 𝑃 ∈ 𝑋 ∧ ∀ 𝑢 ∈ 𝐽 ( 𝑃 ∈ 𝑢 → ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ 𝑢 ) ) ↔ ( 𝐹 ∈ ( 𝑋 ↑pm ℂ ) ∧ 𝑃 ∈ 𝑋 ∧ ∀ 𝑥 ∈ ℝ+ ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) ) ) ) |
| 39 | 2 38 | syl | ⊢ ( 𝜑 → ( ( 𝐹 ∈ ( 𝑋 ↑pm ℂ ) ∧ 𝑃 ∈ 𝑋 ∧ ∀ 𝑢 ∈ 𝐽 ( 𝑃 ∈ 𝑢 → ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ 𝑢 ) ) ↔ ( 𝐹 ∈ ( 𝑋 ↑pm ℂ ) ∧ 𝑃 ∈ 𝑋 ∧ ∀ 𝑥 ∈ ℝ+ ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) ) ) ) |
| 40 | 5 39 | bitrd | ⊢ ( 𝜑 → ( 𝐹 ( ⇝𝑡 ‘ 𝐽 ) 𝑃 ↔ ( 𝐹 ∈ ( 𝑋 ↑pm ℂ ) ∧ 𝑃 ∈ 𝑋 ∧ ∀ 𝑥 ∈ ℝ+ ∃ 𝑦 ∈ ran ℤ≥ ( 𝐹 ↾ 𝑦 ) : 𝑦 ⟶ ( 𝑃 ( ball ‘ 𝐷 ) 𝑥 ) ) ) ) |