options ls = 80 nodate;
libname fu '../../sdata';
data work;
        set fu.kidney;
        if age = 2 then A2 = 1; else A2 = 0;
        if age = 3 then A3 = 1; else A3 = 0;
/*        A2N=A2*neph; */
/*        A3N=A3*neph; */
proc phreg;
        model survt*censor(0)= neph A2 A3 A2*neph A3*neph / covb rl;
run;