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On reverses of some binary operators

Michal Šabo, Peter Strežo (2005)

Kybernetika

The notion of reverse of any binary operation on the unit interval is introduced. The properties of reverses of some binary operations are studied and some applications of reverses are indicated.

On rigid relation principles in set theory without the axiom of choice

Paul Howard, Eleftherios Tachtsis (2016)

Fundamenta Mathematicae

We study the deductive strength of the following statements: 𝖱𝖱: every set has a rigid binary relation, 𝖧𝖱𝖱: every set has a hereditarily rigid binary relation, 𝖲𝖱𝖱: every set has a strongly rigid binary relation, in set theory without the Axiom of Choice. 𝖱𝖱 was recently formulated by J. D. Hamkins and J. Palumbo, and 𝖲𝖱𝖱 is a classical (non-trivial) 𝖹𝖥𝖢-result by P. Vopěnka, A. Pultr and Z. Hedrlín.

On Rough Subgroup of a Group

Xiquan Liang, Dailu Li (2009)

Formalized Mathematics

This article describes a rough subgroup with respect to a normal subgroup of a group, and some properties of the lower and the upper approximations in a group.

On semialgebraic points of definable sets

Artur Piękosz (1998)

Banach Center Publications

We prove that the semialgebraic, algebraic, and algebraic nonsingular points of a definable set in o-minimal structure with analytic cell decomposition are definable. Moreover, the operation of taking semialgebraic points is idempotent and the degree of complexity of semialgebraic points is bounded.

On Semi-Boolean-Like Algebras

Antonio Ledda, Francesco Paoli, Antonino Salibra (2013)

Acta Universitatis Palackianae Olomucensis. Facultas Rerum Naturalium. Mathematica

In a previous paper, we introduced the notion of Boolean-like algebra as a generalisation of Boolean algebras to an arbitrary similarity type. In a nutshell, a double-pointed algebra 𝐀 with constants 0 , 1 is Boolean-like in case for all a A the congruences θ a , 0 and θ a , 1 are complementary factor congruences of 𝐀 . We also introduced the weaker notion of semi-Boolean-like algebra, showing that it retained some of the strong algebraic properties characterising Boolean algebras. In this paper, we continue the investigation...

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