Hi Cromwell, in <boost/mpl/math/rational.hpp> In the definition for mpl::math::rational would it not be better to make the nested type member using the numerator and denominator rather than the input parameters.eg for: typedef rational<integral_c_<int,2>,integral_c<int,8> >::type type; currently type is a rational<integral_c_<int,2>,integral_c<int,8> > in the second case type is a rational<integral_c_<int,1>,integral_c<int,4> > I believe the second is superior. Can supply a patch if you like ... Secondly, are the next and prior members necessary? IMO they only make sense for integers. Thirdly, It should be noted that there is a <boost/mpl/math/rational_c.hpp> header, but as rational_c is defined in <boost/mpl/math/rational.hpp> I think its now both redundant and confusing. Cheers Andy Little