adequate representation

members of a class not present as parties to the litigation may be bound by the judgment where they are in fact adequately represented by parties who are present, or where they actually participate in the conduct of the litigation in which members of the class are present as parties... or where the interest of the members of the class, some of whom are present as parties, is joint, or where for any other reason the relationship between the parties present and those who are absent is such as legally to entitle the former to stand in judgment for the latter