This subclause describes the ratio library. It provides a class template
ratio which exactly represents any finite rational number with a
numerator and denominator representable by compile-time constants of type
intmax_t.

Throughout this subclause, the names of template parameters are used to express
type requirements. If a template parameter is named R1 or R2,
and the template argument is not a specialization of the ratio template,
the program is ill-formed.