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arXiv 2301.02205math.LO
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含蓄否定逻辑

The logic with unsharp implication and negation

Ivan Chajda, Helmut Länger

摘要:

众所周知,直觉主义逻辑可以用Brouwerian半格,即相对伪补半格来形式化。将逻辑连接蕴涵看作是相对伪补,将合取看作是半格运算交。如果Brouwerian半格有一个底元0,则关于0的相对伪补称为伪补,它在这个逻辑中被认为是连接否定。我们的思想是考虑一个任意的交半格,0只满足升链条件,升链条件在有限半格中是平凡满足的,并引入连接否定x^0作为满足x^z=0的所有极大元z的集合和连接蕴涵x->y作为满足x^z \le y的所有极大元z的集合.这样的否定和蕴涵是“不尖锐的”,因为它分别赋予属于半格的一个条目x或两个条目x和y一个子集而不是半格的一个元素。令人惊讶的是,这种否定和蕴涵仍然分别具有直觉主义逻辑中这些连接词的许多性质,特别是推导规则前件式。此外,非尖锐否定和非尖锐蕴涵可以分别用五个和七个简单公理来刻画。提出了几个例子。引入了演绎系统和滤子的概念以及由滤子确定的同余。最后,我们描述了这些概念之间的某些关系。

英文摘要:

It is well-known that intuitionistic logics can be formalized by means of Brouwerian semilattices, i.e. relatively pseudocomplemented semilattices. Then the logical connective implication is considered to be the relative pseudocomplement and conjunction is the semilattice operation meet. If the Brouwerian semilattice has a bottom element 0 then the relative pseudocomplement with respect to 0 is called the pseudocomplement and it is considered as the connective negation in this logic. Our idea is to consider an arbitrary meet-semilattice with 0 satisfying only the Ascending Chain Condition, which is trivially satisfied in finite semilattices, and introduce the connective negation x^0 as the set of all maximal elements z satisfying x^z=0 and the connective implication x->y as the set of all maximal elements z satisfying x^z\le y. Such a negation and implication is "unsharp" since it assigns to one entry x or to two entries x and y belonging to the semilattice, respectively, a subset instead of an element of the semilattice. Surprisingly, this kind of negation and implication, respectively, still shares a number of properties of these connectives in intuitionistic logic, in particular the derivation rule Modus Ponens. Moreover, unsharp negation and unsharp implication can be characterized by means of five, respectively seven simple axioms. Several examples are presented. The concepts of a deductive system and of a filter are introduced as well as the congruence determined by such a filter. We finally describe certain relationships between these concepts.

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