Description: The outer measure of a set is a nonnegative extended real. (Contributed by Glauco Siliprandi, 17-Aug-2020)
Ref | Expression | ||
---|---|---|---|
Hypotheses | omecl.o | ⊢ ( 𝜑 → 𝑂 ∈ OutMeas ) | |
omecl.x | ⊢ 𝑋 = ∪ dom 𝑂 | ||
omecl.ss | ⊢ ( 𝜑 → 𝐴 ⊆ 𝑋 ) | ||
Assertion | omecl | ⊢ ( 𝜑 → ( 𝑂 ‘ 𝐴 ) ∈ ( 0 [,] +∞ ) ) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | omecl.o | ⊢ ( 𝜑 → 𝑂 ∈ OutMeas ) | |
2 | omecl.x | ⊢ 𝑋 = ∪ dom 𝑂 | |
3 | omecl.ss | ⊢ ( 𝜑 → 𝐴 ⊆ 𝑋 ) | |
4 | 1 2 | omef | ⊢ ( 𝜑 → 𝑂 : 𝒫 𝑋 ⟶ ( 0 [,] +∞ ) ) |
5 | 2 | a1i | ⊢ ( 𝜑 → 𝑋 = ∪ dom 𝑂 ) |
6 | 1 | dmexd | ⊢ ( 𝜑 → dom 𝑂 ∈ V ) |
7 | 6 | uniexd | ⊢ ( 𝜑 → ∪ dom 𝑂 ∈ V ) |
8 | 5 7 | eqeltrd | ⊢ ( 𝜑 → 𝑋 ∈ V ) |
9 | 8 3 | ssexd | ⊢ ( 𝜑 → 𝐴 ∈ V ) |
10 | elpwg | ⊢ ( 𝐴 ∈ V → ( 𝐴 ∈ 𝒫 𝑋 ↔ 𝐴 ⊆ 𝑋 ) ) | |
11 | 9 10 | syl | ⊢ ( 𝜑 → ( 𝐴 ∈ 𝒫 𝑋 ↔ 𝐴 ⊆ 𝑋 ) ) |
12 | 3 11 | mpbird | ⊢ ( 𝜑 → 𝐴 ∈ 𝒫 𝑋 ) |
13 | 4 12 | ffvelrnd | ⊢ ( 𝜑 → ( 𝑂 ‘ 𝐴 ) ∈ ( 0 [,] +∞ ) ) |