n_evolution">2</a>], the error
can be caught by exercising all of the requirements needed by the
function template.  Exactly how the requirements (the valid
expressions in particular) are exercised is a tricky issue, since we
want the code to be compiled --- <i>but not executed</i>.  Our
approach is to exercise the requirements in a separate function that
is assigned to a function pointer.  In this case, the compiler will
instantiate the function but will not actually invoke it.  In
addition, an optimizing 