Ci( z, b, n, k ) = { local( c = 1 );
    n--; k--;
    while( k >= 0 ,
        if( z < b,
            print1(c, " ");
            c++;
            if( n > 0,
                b = b*k \ n);
            n--; k--;
        ,
            c++;
            z -= b;
            b = b*(n-k)\n;
            n--
        )
    );
	print;
}

combI( n, k ) = {
    local(  bnk = binomial( n, k ),
            b11 = bnk * k \ n );            \\ binomial( n-1, k-1 )
    for( z = 0, bnk - 1,
        Ci(z,   b11,   n, k ) );
}