A notion of closure operator with respect to a functor U is introduced. This allows us to describe a number of mathematical constructions that could not be described by means of the already existing notion of closure operator. Some basic results and examples are provided. Mathematics Subject Classification (1991). 18A22, 18A32, 06A15.

In this talk I will give a overview on the connections between closure operators and choice operators and on related results. An operator on a finite set S is a map defined on the set P(S) of all the subsets of S. A closure operator is an extensive, isotone and idempotent operator. A choice operator c is a contracting operator (c(A) ⊆ A, for every A ⊆ S). Choice operators and their lattices hav...

The least common ancestor on two vertices, denoted , , is a well defined operation in a directed acyclic graph (dag) . We introduce , a natural extension of , for any set of vertices. Given such a set , one can iterate in order to obtain an increasing set sequence. being finite, this sequence has always a limit which defines a closure operator. Two equivalent definitions of this operator are gi...

BACKGROUND The purpose of this study was to investigate the association of a novel biometric parameter, relative lens vault (LV), with primary angle-closure (PAC) and primary angle-closure glaucoma (PACG). METHODS We evaluated 101 subjects with PAC (G) and 101 normal subjects that were age- and gender-matched. Based on anterior-segment optical coherence tomography scans, and using customized ...

The distribution function for the first eigenvalue spacing in the Laguerre unitary ensemble of finite size may be expressed in terms of a solution of the fifth Painlevé transcendent. The generating function of a certain discontinuous linear statistic of the Laguerre unitary ensemble can similarly be expressed in terms of a solution of the fifth Painlevé equation. The methodology used to derive ...

We consider the question of taking transitive closures on top of pure relational systems (Sybase and Ingres in this case). We developed three kinds of transitive closure programs , one using a stored procedure to simulate a built-in transitive closure operator, one using the C language embedded with SQL statements to simulate the iterated execution of the transitive closure operation, and one u...