#include <triqs/clef.hpp>
#include <triqs/statistics.hpp>
using namespace triqs::statistics;
int main() {
 observable<double> X;
 X << 1.0;
 X << -1.0;
 X << .5;
 X << .0;
 std::cout << average_and_error(X) << std::endl;
 std::cout << average_and_error(X * X) << std::endl;
 return 0;
}