mathlib

c5b6fe54 - feat(analysis/locally_convex/basic): a few lemmas about balanced sets (#14876)

feat(analysis/locally_convex/basic): a few lemmas about balanced sets (#14876) Add new lemmas about unions and intersection and membership of balanced sets. Co-authored-by: Yaël Dillies <yael.dillies@gmail.com> Co-authored-by: YaelDillies <yael.dillies@gmail.com> Co-authored-by: Yaël Dillies <yael.dillies@gmail.com>