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In the older literature they use the term integral rational function. I did google search, math/SE search etc and see that mostly integral rational function is interpreted to mean "polynomial".

But when we read in the older literature that the integral rational function $f=f(x_1,x_2,...,x_n)$ is required to be homogeneous of degree zero in the $x_k$'s, shouldn't it have the form

$$f=\frac{x_9}{x_{15}}$$ or $$f=\frac{x_1 x_5}{x_2 x_7}+\left( \frac{x_1 x_2 x_3}{x_4 x_5 x_6} \right)^3$$

for example? It seems the only way it is homogeneous of degree zero is to have fractions appear in $f$.

The problem I see is that a polynomial by definition does not have variables in the denominator.

Is then an integral rational function always a polynomial? What are the properties of integral rational functions.

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    $\begingroup$ The answers to your two questions are no, and too long to answer for a single question. $\endgroup$ – Don Thousand Sep 12 '19 at 15:38
  • $\begingroup$ Which literature are you referring to? $\endgroup$ – Chappers Sep 12 '19 at 15:39
  • $\begingroup$ Don Thousand, the two examples I gave, are they correct examples of homogeneous integral rational functions of degree 0? $\endgroup$ – user142523 Sep 12 '19 at 17:08
  • $\begingroup$ Chappers, older literature that refers to homogeneous integral rational functions,, the American Journal of Math from the early 1900s has articles that use this term $\endgroup$ – user142523 Sep 12 '19 at 17:16
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    $\begingroup$ Relevant: math.stackexchange.com/questions/1275194/… $\endgroup$ – Chappers Sep 12 '19 at 17:26

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