restart; t:=n->t0+n*h; t(2); p:=x->f(t(n-1),ynm1)*(x-t(n))*(x-t(n+1))/((t(n-1)-t(n))*(t(n-1)-t(n+1))) +f(t(n),yn)*(x-t(n-1))*(x-t(n+1))/((t(n)-t(n-1))*(t(n)-t(n+1))) +f(t(n+1),ynp1)*(x-t(n-1))*(x-t(n))/((t(n+1)-t(n-1))*(t(n+1)-t(n))); simplify(p(x)); sort(simplify(int(p(x),x=t(n)..t(n+1))));