T in { [t,Y] where t is Element of Toler_on_subsets X, Y is Subset of X : t is Tolerance of Y } ;
then consider t being Element of Toler_on_subsets X, Y being Subset of X such that
A1: ( T = [t,Y] & t is Tolerance of Y ) ;
thus T `2 is Subset of X by A1, MCART_1:def 2; :: thesis: verum