Metamath Proof Explorer


Theorem ovnxrcl

Description: The Lebesgue outer measure of a set is an extended real. (Contributed by Glauco Siliprandi, 11-Oct-2020)

Ref Expression
Hypotheses ovnxrcl.1
|- ( ph -> X e. Fin )
ovnxrcl.2
|- ( ph -> A C_ ( RR ^m X ) )
Assertion ovnxrcl
|- ( ph -> ( ( voln* ` X ) ` A ) e. RR* )

Proof

Step Hyp Ref Expression
1 ovnxrcl.1
 |-  ( ph -> X e. Fin )
2 ovnxrcl.2
 |-  ( ph -> A C_ ( RR ^m X ) )
3 iccssxr
 |-  ( 0 [,] +oo ) C_ RR*
4 1 2 ovncl
 |-  ( ph -> ( ( voln* ` X ) ` A ) e. ( 0 [,] +oo ) )
5 3 4 sseldi
 |-  ( ph -> ( ( voln* ` X ) ` A ) e. RR* )