mathlib

26710686 - feat(data/set/intervals): add 2 Icc ssubset lemmas (#5617)

feat(data/set/intervals): add 2 Icc ssubset lemmas (#5617) Add two strict subset lemmas for Icc, discussed in https://leanprover.zulipchat.com/#narrow/stream/116395-maths/topic/Icc_ssubset_Icc. Co-authored-by: Damiano Testa