<=>

        # Rational.<=>

(from ruby core)
---
    rational <=> numeric  ->  -1, 0, +1, or nil

---

Returns -1, 0, or +1 depending on whether `rational` is less than, equal
to, or greater than `numeric`.

`nil` is returned if the two values are incomparable.

    Rational(2, 3) <=> Rational(2, 3)  #=> 0
    Rational(5)    <=> 5               #=> 0
    Rational(2, 3) <=> Rational(1, 3)  #=> 1
    Rational(1, 3) <=> 1               #=> -1
    Rational(1, 3) <=> 0.3             #=> 1

    Rational(1, 3) <=> "0.3"           #=> nil