/// A fraction `p`/`q` with integers `p` and `q`.
///
/// `p` is called the numerator and `q` is called the denominator.
pub trait Fraction<T>: Sized {
    /// Returns the numerator `p`
    fn numerator(&self) -> T;
    /// Returns the denominator `q`
    fn denominator(&self) -> T;

    /// Returns the multiplicative inverse `q/p` for fraction `p/q`.
    ///
    /// If `p` is zero, None is returned.
    fn inv(&self) -> Option<Self>;
}