#include <triqs/clef.hpp>
#include <vector>
using namespace triqs::clef;
int main() {
 placeholder<0> i_;
 placeholder<1> x_;
 placeholder<2> y_;
 std::vector<int> V;

 // arithmetic
 auto e = x_ + 2 * y_;

 // simple math function
 auto e1 = cos(2 * x_ + 1);
 auto e2 = abs(2 * x_ - 1);

 // making V lazy
 auto e0 = make_expr(V)[i_];
}