sum1(a_*b_,k_):=if(hasnot(a,k), a*sum1(b,k));
sum1(a_+b_,k_):=sum1(a,k)+sum1(b,k);
sum1(x_,x_):=(x^2-x)/2;
sum1(x_^2,x_):=1/6*x-9/18*x^2+1/3*x^3;
sum1(x_^3,x_):=1/4* (x - 1)^2* x^2;

sum1(y_):=sum1(y,k);