Metamath Proof Explorer


Theorem von0val

Description: The Lebesgue measure (for the zero dimensional space of reals) of every measurable set is zero. (Contributed by Glauco Siliprandi, 8-Apr-2021)

Ref Expression
Hypothesis von0val.1 ( 𝜑𝐴 ∈ dom ( voln ‘ ∅ ) )
Assertion von0val ( 𝜑 → ( ( voln ‘ ∅ ) ‘ 𝐴 ) = 0 )

Proof

Step Hyp Ref Expression
1 von0val.1 ( 𝜑𝐴 ∈ dom ( voln ‘ ∅ ) )
2 0fin ∅ ∈ Fin
3 2 a1i ( 𝜑 → ∅ ∈ Fin )
4 3 1 mblvon ( 𝜑 → ( ( voln ‘ ∅ ) ‘ 𝐴 ) = ( ( voln* ‘ ∅ ) ‘ 𝐴 ) )
5 3 1 vonmblss2 ( 𝜑𝐴 ⊆ ( ℝ ↑m ∅ ) )
6 5 ovn0val ( 𝜑 → ( ( voln* ‘ ∅ ) ‘ 𝐴 ) = 0 )
7 4 6 eqtrd ( 𝜑 → ( ( voln ‘ ∅ ) ‘ 𝐴 ) = 0 )