∀ {α : Type u_2} [inst : Preorder α] [inst_1 : AddCommSemigroup α] [inst_2 : Sub α] [inst_3 : OrderedSub α]
  [inst_4 : AddLeftMono α] (s t : NonemptyInterval α), (s - t).toProd.1 = s.toProd.1 - t.toProd.2