no goals
α : Type u_1
inst✝¹ : LinearOrder α
inst✝ : LocallyFiniteOrder α
a✝ b✝ c✝ d a b c : α
hab : a ≤ b
hbc : b ≤ c
⊢ Ico a b + Ico b c = Ico a c
rw [add_eq_union_iff_disjoint.2 (Ico_disjoint_Ico le_rfl), Ico, Ico, Ico, ← Finset.union_val,
  Finset.Ico_union_Ico_eq_Ico hab hbc]