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On the Generalization of Hilbert’s 17th Problem and Pythagorean Fields ()

The notion of
preordering, which is a generalization of the notion of ordering, has been
introduced by Serre. On the other hand, the notion of round quadratic forms has
been introduced by Witt. Based on these ideas, it is here shown that 1) a field ** F** is formally real

*n*-pythagorean iff the

*n*th radical,

*R*is a preordering (Theorem 2), and 2) a field

_{n}F**is**

*F**n*-pythagorean iff for any

*n*-fold Pfister form

**. There exists an odd integer l(**

*ρ***>**1) such that l×

*ρ***is a round quadratic form (Theorem 8). By considering upper bounds for the number of squares on Pfister’s interpretation, these results finally lead to the main result (Theorem 10) such that the generalization of pythagorean fields coincides with the generalization of Hilbert’s 17th Problem.**

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*Advances in Pure Mathematics*, Vol. 3 No. 7A, 2013, pp. 1-4. doi: 10.4236/apm.2013.37A001.

Conflicts of Interest

The authors declare no conflicts of interest.

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