These are BigFractions. What are a, b, c and d?
BigIntegers
        a         c
      -----  vs ----      (vs is > < >= <= != ==)
        b         d


        ad  vs  bc         multipy both sides by bd which is > 0.

        ad - bc vs 0


        a.multiply(d).subtract( b.multiply(c) ) vs 0

        (a.multiply(d).subtract(b.multiply(c))).compareTo(BigInteger.ZERO)