∀ {α : Type u_1} {β : Type u_2} [inst : Preorder α] [inst_1 : Preorder β] [inst_2 : LocallyFiniteOrder α]
  [inst_3 : LocallyFiniteOrder β] [inst_4 : LocallyFiniteOrderTop α] [inst_5 : LocallyFiniteOrderBot β] (a : α) (b : β),
  Finset.Ioc (Sum.inlₗ a) (Sum.inrₗ b) = Finset.map toLex.toEmbedding ((Finset.Ioi a).disjSum (Finset.Iic b))