∀ {α : Type u_1} [inst : Add α] [inst_1 : Preorder α] [inst_2 : DecidableEq α] [AddLeftMono α] [AddRightMono α]
  [inst_5 : LocallyFiniteOrderTop α] (a b : α), Finset.Ici a + Finset.Ici b ⊆ Finset.Ici (a + b)