Metamath Proof Explorer


Theorem omecl

Description: The outer measure of a set is a nonnegative extended real. (Contributed by Glauco Siliprandi, 17-Aug-2020)

Ref Expression
Hypotheses omecl.o ( 𝜑𝑂 ∈ OutMeas )
omecl.x 𝑋 = dom 𝑂
omecl.ss ( 𝜑𝐴𝑋 )
Assertion omecl ( 𝜑 → ( 𝑂𝐴 ) ∈ ( 0 [,] +∞ ) )

Proof

Step Hyp Ref Expression
1 omecl.o ( 𝜑𝑂 ∈ OutMeas )
2 omecl.x 𝑋 = dom 𝑂
3 omecl.ss ( 𝜑𝐴𝑋 )
4 1 2 omef ( 𝜑𝑂 : 𝒫 𝑋 ⟶ ( 0 [,] +∞ ) )
5 2 a1i ( 𝜑𝑋 = dom 𝑂 )
6 1 dmexd ( 𝜑 → dom 𝑂 ∈ V )
7 6 uniexd ( 𝜑 dom 𝑂 ∈ V )
8 5 7 eqeltrd ( 𝜑𝑋 ∈ V )
9 8 3 ssexd ( 𝜑𝐴 ∈ V )
10 elpwg ( 𝐴 ∈ V → ( 𝐴 ∈ 𝒫 𝑋𝐴𝑋 ) )
11 9 10 syl ( 𝜑 → ( 𝐴 ∈ 𝒫 𝑋𝐴𝑋 ) )
12 3 11 mpbird ( 𝜑𝐴 ∈ 𝒫 𝑋 )
13 4 12 ffvelrnd ( 𝜑 → ( 𝑂𝐴 ) ∈ ( 0 [,] +∞ ) )