class Foo {
  func a<T>(_ val: T) -> String { return "not equatable" }
  func a<T: Equatable>(_ val: T) -> String { return "equatable" }
}

class Bar: Foo {
  // these work like a charm
  func b<T>(_ val: T) -> String { return super.a(val) }
  func b<T: Equatable>(_ val: T) -> String { return super.a(val) }

  // "declaration 'a' cannot override more than one superclass declaration"
  override func a<T>(_ val: T) -> String { return super.a(val) }
  override func a<T: Equatable>(_ val: T) -> String { return super.a(val) }
}

let bar = Bar()
bar.b(1) // "equatable"
bar.b(Int.self) // "not equatable"