mathlib

396487f9 - feat(topology/separation): Adds t2_space instances for disjoint unions (sums and sigma types). (#5113)

feat(topology/separation): Adds t2_space instances for disjoint unions (sums and sigma types). (#5113) Co-authored-by: Yury G. Kudryashov <urkud@urkud.name> Co-authored-by: Adam Topaz <adamtopaz@users.noreply.github.com>