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arXiv 1805.02458math.RA
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3-分配簇中的关系恒等式

Relation identities in 3-distributive varieties

Paolo Lipparini

摘要:

令$α$、$β$、$γ, \dots$ $Θ$、$Ψ, \dots$ $R$、$S$、$T, \dots$分别为同余、容差和自反容许关系的变量。并置表示相交。证明了如果恒等式$α(β\circ Θ) \subseteq αβ\circ αΘ\circ αβ$在一个簇$\mathcal {V}$中成立,则$\mathcal {V}$有多数项,等价地,$\mathcal {V}$满足$ α(β\circ γ) \subseteq αβ\circ αγ$ .结果是出乎意料的,因为在所显示的恒等式中,我们在右边多了一个因子,而且,如果我们让$Θ$是一个同余,我们得到一个等价于$3$ -分配性的条件,众所周知,它严格弱于多数项的存在。上述结果在许多意义上都是最优的,例如,我们证明了在每个$3$分布簇中,所显示的恒等式(如$ R (S \circ γ) \subseteq R S \circ R γ\circ R S$或$R(S \circ T) \subseteq R S \circ RT \circ RT \circ RS$)的微小变化都成立。类似的身份是有效的,甚至在品种与$2$ Gumm条款,没有分配假设。我们还讨论了$n$ -置换簇中的关系恒等式,并给出了一些关于蕴涵代数的注记。

英文摘要:

Let $α$, $β$, $γ, \dots$ $Θ$, $Ψ, \dots$ $R$, $S$, $T, \dots$ be variables for, respectively, congruences, tolerances and reflexive admissible relations. Let juxtaposition denote intersection. We show that if the identity $α(β\circ Θ) \subseteq αβ\circ αΘ\circ αβ$ holds in a variety $\mathcal {V}$, then $\mathcal {V}$ has a majority term, equivalently, $\mathcal {V}$ satisfies $ α(β\circ γ) \subseteq αβ\circ αγ$. The result is unexpected, since in the displayed identity we have one more factor on the right and, moreover, if we let $Θ$ be a congruence, we get a condition equivalent to $3$-distributivity, which is well-known to be strictly weaker than the existence of a majority term. The above result is optimal in many senses, for example, we show that slight variations on the displayed identity, such as $ R (S \circ γ) \subseteq R S \circ R γ\circ R S$ or $R(S \circ T) \subseteq R S \circ RT \circ RT \circ RS$ hold in every $3$-distributive variety. Similar identities are valid even in varieties with $2$ Gumm terms, with no distributivity assumption. We also discuss relation identities in $n$-permutable varieties and present a few remarks about implication algebras.

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