∀ {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] (a₁ a₂ : α),
  Finset.Ioc (Sum.inlₗ a₁) (Sum.inlₗ a₂) =
    Finset.map (Function.Embedding.inl.trans toLex.toEmbedding) (Finset.Ioc a₁ a₂)