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20122026
most citedPartial Derivative Automaton for Regular Expressions with Shuffle

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math.NT2026

Metaconjugation and Quadratic Forms

Adriana Cardoso, António Leite, António Machiavelo +2

We present a quaternionic proof that the quadratic form represents all positive integers, and that the form represents all natural numbers…

math.NT2025

The Dedekind-Hasse Criterion in Quaternion Algebras

Adriana Cardoso, António Machiavelo

We show that a criterion for an integral domain to be a principal ideal domain (PID), due to Dedekind and Hasse, can also be applied in quaternion orders, and that it can be used t…

math.NT2025

On the Cycle Structure of the Metacommutation Map

António Leite, António Machiavelo

Cohn and Kumar showed that the permutation on the set of the classes of left associated Hurwitz primes above an odd prime induced through metacommutation by a Hurwitz prime …

math.NT2020

Report on Zhi-Wei Sun's "1-3-5 conjecture" and some of its refinements

António Machiavelo, Rogério Reis, Nikolaos Tsopanidis

We report here on the computational verification of a refinement of Zhi-Wei Sun's "1-3-5 conjecture" for all natural numbers up to 105 103 560 126. This, together with a result of…

math.NT2020

Zhi-Wei Sun's 1-3-5 Conjecture and Variations

António Machiavelo, Nikolaos Tsopanidis

In this paper, using quaternion arithmetic in the ring of Lipschitz integers, we present a proof of Zhì-Wěi Sūn's "1-3-5 conjecture" for integral solutions, and for all natural num…

math.NT2012

Dynamics of a quasi-quadratic map

Assis Azevedo, Maria Carvalho, António Machiavelo

We consider the map X defined on the rational numbers given by x --> x * ceil(x), where ceil(x) denotes the smallest integer greater than or equal to x, and study the problem of fi…

math.NT2012

Some Connections Between The Arithmetic and The Geometry of Lipschitz Integers

António Machiavelo, Luís Roçadas

Some relationships between the arithmetic and the geometry of Lipschitz and Hurwitz integers are presented. In particular, it is shown that the (ternary) vector product of a Lipsch…