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Campillo, Antonio and Ruiz Sancho, Jesús María
(1990)
*Some remarks on pythagorean real curve germs.*
Journal of Algebra, 128
(2).
pp. 271-275.
ISSN 0021-8693

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Official URL: http://www.sciencedirect.com/science/article/pii/002186939090021F

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## Abstract

Let k be a real closed field. A real AP-curve (over k) is a 1-dimensional, excellent Henselian local real domain with residue field k. A 1-dimensional Noetherian local ring is Arf, if emb dim(B)=mult(B) for every local ring B infinitely near to A [ J. Lipman , Amer. J. Math. 93 (1971), 649–685]. For n≥1, the 2nth Pythagoras number p2n of a commutative ring A is the least p, 1≤p≤+∞, such that any sum of 2nth powers in A is a sum of no more than p2nth powers in A. A main purpose of this paper is to affirm the following conjectures proposed by Ruiz [J. Algebra 94 (1985), no. 1, 126–144]: Let A be a real AP-curve, and let A be Pythagorean (i.e., p2=1). Then (i) A is Arf. (ii) Every local ring infinitely near to A is Pythagorean. Actually, the authors obtain a finer result: For a real AP-curve A, the following assertions are equivalent: (1) A is Arf; (2) A is Pythagorean; (3) p2n=1 for some n; (4) p2n=1 for all n. Here, (2)(1) is exactly Conjecture (i) and (1)(2) reduces Conjecture (ii) to the obvious fact that, if A is Arf, every local ring infinitely near to A is Arf too. Of course, the result contains some additional insight into the study of Pythagoras's numbers, even of higher order, of real curve germs.

Item Type: | Article |
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Uncontrolled Keywords: | Arf domain; pythagorean real curve germ |

Subjects: | Sciences > Mathematics > Number theory Sciences > Mathematics > Algebraic geometry |

ID Code: | 19982 |

Deposited On: | 15 Feb 2013 17:34 |

Last Modified: | 12 Dec 2018 15:13 |

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