n=-2:10;
x=[1:7,6:-1:1]
[x21,n21]=sigfold(x,n)
[x21,n21]=sigshift(x21,n21,3)
[x22,n22]=sigshift(x,n,2)
[x22,n22]=sigmult(x,n,x22,n22)
[x2,n2]=sigadd(x21,n21,x22,n22);
subplot(2,1,2);stem(n2,x2);
   title('sequency in example 2.2b')
   xlabel('n');
   ylabel('x2(n)');