'' ... where two or more persons are bound together for one or more common purposes by mutual undertakings , each having mutual duties and obligations , in an organization which has rules identifying in whom control of the organization and its funds is vested , and which can be joined or left at will . '' '' ... where two or more persons are bound together for one or more common purposes by mutual undertakings , each having mutual duties and obligations , in an organization which has rules identifying in whom control of the organization and its funds are vested , and which can be joined or left at will . ''