public static NestedListNode <T> NodeAt <T>(this NestedListNode <T> start, Numeral index) =>
 ChurchNestedList <T> .NodeAt(start)(index);
 public static T Value <T>(this NestedListNode <T> node) => ChurchNestedList <T> .Value(node);
 public static NestedListNode <T> Next <T>(this NestedListNode <T> node) => ChurchNestedList <T> .Next(node);
 public static Boolean IsNull <T>(this NestedListNode <T> node) => ChurchNestedList <T> .IsNull(node);