   /// - Returns: `true` if the set has no elements in common with `other`;
   ///   otherwise, `false`.
   @inlinable
-  public func isDisjoint<S: Sequence>(with other: __owned S) -> Bool
+  public func isDisjoint<S: Sequence>(with other: S) -> Bool
   where S.Element == Element {
     // FIXME(performance): Don't need to build a set.
     let otherSet = Set(other)

  /// - Returns: `true` if the set is a subset of `possibleSuperset`;
  ///   otherwise, `false`.
  @inlinable
  public func isSubset<S: Sequence>(of possibleSuperset: __owned S) -> Bool
  where S.Element == Element {
    // FIXME(performance): isEmpty fast path, here and elsewhere.
    let other = Set(possibleSuperset)

  /// - Returns: `true` is the set is strict subset of
  ///   `possibleStrictSuperset`; otherwise, `false`.
  @inlinable
  public func isStrictSubset<S: Sequence>(of possibleStrictSuperset: S) -> Bool
  where S.Element == Element {
    // FIXME: code duplication.
    let other = Set(possibleStrictSuperset)
