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### `nm`, `dn`

`nm(rat)`
  :: Numerator of rat.
`dn(rat)`
  :: Denominator of rat.

return
  integer or polynomial
rat
  rational number or rational expression

- Numerator and denominator of a given rational expression.
- For a rational number, they return its numerator and denominator, respectively. For a rational expression whose numerator and denominator may contain rational numbers, they do not separate those rational coefficients to numerators and denominators.
- For a rational number, the denominator is always kept positive, and the sign is contained in the numerator.
- Risa/Asir does not cancel the common divisors unless otherwise explicitly specified by the user. Therefore, `nm()` and `dn()` return the numerator and the denominator as it is, respectively.

    [2] [nm(-43/8),dn(-43/8)];
    [-43,8]
    [3] dn((x*z)/(x*y));
    y*x
    [3] dn(red((x*z)/(x*y)));
    y

`References`
  section `red`.

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