∀ {α : Type u_1} [inst : AddCommSemigroup α] [inst_1 : PartialOrder α] [ExistsAddOfLE α] [AddLeftMono α]
  [inst_4 : Sub α] [OrderedSub α] {a b c : α}, AddLECancellable (a - b) → b ≤ a → c < b → a - b < a - c