It would be a quartic function, huh ?

But yeah,

*this* is true

While dealing with functions which are defined to be polynomials, yep.

But since you were talking about $\displaystyle f^{-1}$, it just didn't make sense... for me at least..perhaps it is different for someone else >.<

I don't really agree with that... Because it would mean that the inverse function is also a polynomial... Prove it ? =)

Plus, like I said, the degree of a polynomial is an

*integer* (it was quoted from Wikipedia)

Polynomial - Wikipedia, the free encyclopedia << they also give examples which are not polynomials.