         }
     }
     
+    /// Remove all elements.
+    ///
+    /// - parameter keepCapacity: If `true`, the operation preserves the
+    ///   storage capacity that the collection has, otherwise the underlying
+    ///   storage is released.  The default is `false`.
+    ///
+    /// - Complexity: O(`count of nodes`).
     public mutating func removeAll(keepCapacity: Bool = false) {
         table.removeAll(keepCapacity: keepCapacity)
     }

    }
    
    /// A set containing just the nodes of `self`.
    public var nodes: Set<Node> {
        var _nodes = Set<Node>()
        for (_node, list) in table {

        return nil
    }
    
    /// `true` iff `self` contains `node`.
    ///
    /// - Complexity: O(`count of nodes`).
    @warn_unused_result
    public func contains(node: Node) -> Bool {
        for (_node, list) in table where _node == node || list.keys.contains(node) {
