# File provisioningapi.rb, line 481
                def is_member(email_address, group_id)
                        xml_response = request(:membership_confirm, group_id+'/member/'+email_address, @headers)
                        # if the email_address is not member of the group, an error is raised, otherwise true is returned 
                        return true

                        rescue GDataError => e
                        return false if e.reason.eql?("EntityDoesNotExist")
                end