Closure is a fundamental property of many discrete systems. Transitive closure in relations has been well studied, e.g. 1,14,6,5], as has geometric closure 8,9] and closure in various kinds of graphs 17,10]. The closed sets of a closure operator illustrate a kind of well-behaved internal structure that is the main theme of this paper. In Section 1, we examine antimatroid closure spaces. In Sect...

The paper presents a new definition of closure operator which encompasses the standard Dikranjan-Giuli notion, as well as the Bourn-Gran notion of normal closure operator. As is well known, any two closure operators C,D in a category may be composed in two ways: For a subobject M → X one may consider DX(CXM) or DCX(M)(M) as the value at M of a new closure operator D ·C or D ∗C, respectively. Th...

Gap-definability and the gap closure operator were defined by S. Fenner, L. Fortnow and S. Kurth (J. Comput. System Sci. 48, 116 148 (1994)). Few complexity classes were known at that time to be gapdefinable. In this paper, we give simple characterizations of both gapdefinability and the gap-closure operator, and we show that many complexity classes are gap-definable, including P, P, PSPACE, EX...

Let Tf denote the Toeplitz operator with symbol function f on the Bergman space La(B, dv) of the unit ball in C . It is a natural problem in the theory of Toeplitz operators to determine the norm closure of the set {Tf : f ∈ L∞(B, dv)} in B(La(B, dv)). We show that the norm closure of {Tf : f ∈ L∞(B, dv)} actually coincides with the Toeplitz algebra T , i.e., the C∗-algebra generated by {Tf : f...

Closure operators defined on various sets (set of all classical fuzzy sets, set of all semi-cuts, set of all cuts in a Q-set, etc.) are investigated and it is shown how a closure operator defined on one set can be extended to a closure operator defined on another set.

The lattice of closed subsets of a set under such a closure operator is semimodular. Perhaps the best known example of a closure operator satisfying the exchange principle is the closure operator on a vector space W where for X ___ W we let C(X) equal the span of X. The lattice of C-closed subsets of W is isomorphic to Con(W) in a natural way; indeed, if Y _~ W x W and Cg(Y) denotes the congrue...

in this paper, we introduce the notion of multiplier in -algebra and study relationships between multipliers and some special mappings, likeness closure operators, homomorphisms and ( -derivations in -algebras. we introduce the concept of idempotent multipliers in bl-algebra and weak congruence and obtain an interconnection between idempotent multipliers and weak congruences. also, we introduce...

We introduce the notion of weak convexity in metric spaces, a generalization ordinary commonly used machine learning. It is shown that weakly convex sets can be characterized by closure operator and have unique decomposition into set pairwise disjoint connected blocks. give two generic efficient algorithms, an extensional intensional one for learning concepts study their formal properties. Our ...

In this paper definitions of many sorted closure system and many sorted closure operator are introduced. These notations are also introduced in [9], but in another meaning. In this article closure system is absolutely multiplicative subset family of many sorted sets and in [9] is many sorted absolutely multiplicative subset family of many sorted sets. Analogously, closure operator is function b...