Function square

Examples/NoModules/Chapter 11/Ex11_06/Ex11_06.cpp:9–9

the square root of 2

{
  const double sqrt2{ 1.414213562373095 };      // the square root of 2
  auto square(const auto& x) { return x * x; }
  auto pow4(const auto& x) { return square(square(x)); }
}