Here's a version of the patch that adds exact comparisons between the various numeric types.  The only slightly tricky comparison is the Fraction <-> Decimal one:  an obvious strategy is to convert the Decimal exactly to a Fraction and then use the fraction comparison, but this is inefficient for Decimal instances with large exponent.  So instead, we compare a Decimal `x` with a Fraction `n/d` by comparing `x*d` with `n` in the Decimal domain.