Description: The Lebesgue outer measure of a set is a nonnegative extended real. (Contributed by Glauco Siliprandi, 11-Oct-2020)
Ref | Expression | ||
---|---|---|---|
Hypotheses | ovncl.1 | ||
ovncl.2 | |||
Assertion | ovncl |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | ovncl.1 | ||
2 | ovncl.2 | ||
3 | 1 | ovnf | |
4 | ovexd | ||
5 | 4 2 | ssexd | |
6 | elpwg | ||
7 | 5 6 | syl | |
8 | 2 7 | mpbird | |
9 | 3 8 | ffvelrnd |