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Relative universality and universality obtained by adding constants
Authors:Marie?Demlová  Václav?Koubek  Email author" target="_blank">Ji?í?SichlerEmail author
Institution:1.Department of Mathematics, Faculty of Electrical Engineering,Czech Technical University,Praha 6,Czech Republic;2.Department of Theoretical Computer Science and Mathematical Logic and Institute of Theoretical Computer Science, Faculty of Mathematics and Physics,Charles University,Praha 1,Czech Republic;3.Department of Mathematics,University of Manitoba,Winnipeg,Canada
Abstract:A variety ${\mathbb{V}}${\mathbb{V}} is var-relatively universal if it contains a subvariety \mathbbW{\mathbb{W}} such that the class of all homomorphisms that do not factorize through any algebra in \mathbbW{\mathbb{W}} is algebraically universal. And \mathbbV{\mathbb{V}} has an algebraically universal α-expansion a\mathbbV{\alpha\mathbb{V}} if adding α nullary operations to all algebras in \mathbbV{\mathbb{V}} gives rise to a class a\mathbbV{\alpha\mathbb{V}} of algebras that is algebraically universal. The first two authors have conjectured that any varrelative universal variety \mathbbV{\mathbb{V}} has an algebraically universal α-expansion a\mathbbV{\alpha\mathbb{V}} . This note contains a more general result that proves this conjecture.
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