*Correspondence: [email protected] Department of Mathematics and Applied Physics, Rzeszów University of Technology, P.O. Box 85, Rzeszów, Poland Abstract We present an analog of Banach’s fixed point theorem for CJM contractions in preordered metric spaces. These results substantially extend theorems of Ran and Reurings’ (Proc. Am. Math. Soc. 132(5): 1435-1443, 2003) and Nieto and Rodríguez-Ló...

A characterization of descent morphism in the category of Priestley spaces, as well as necessary and sufficient conditions for such morphisms to be effective are given. For that we embed this category in suitable categories of preordered topological spaces were descent and effective morphisms are described using the monadic description of descent.

If (L,∨,∧, 0, 1, ) is a complete ortholattice, f : Ln → L any partial function, then there is a complete ortholattice L containing L as a subortholattice, and a ortholattice polynomial p with coefficients in L such that p(a1, . . . , an) = f(a1, . . . , an) for all a1, . . . , an ∈ L. Iterating this construction long enough yields a complete ortholattice in which every function can be interpola...

for a graph g, let d(g) be the set of all strong orientations of g. the orientationnumber of g is min {d(d) |d belongs to d(g)}, where d(d) denotes the diameterof the digraph d. in this paper, we determine the orientation number for some subgraphs of complete bipartite graphs.

Maude modules can be understood as models that can be formally analyzed and verified with respect to different properties expressing various formal requirements. However, Maude lacks the formal tools to perform some of these analyses and thus they can only be done by hand. The Heterogeneous Tool Set Hets is an institution-based combination of different logics and corresponding rewriting, model ...

For a function f of one preordered set X to another Y , we shall establish several consequences of the following two definitions: (a) f is increasingly φ–regular, for some function φ of X to itself, if for any x1 , x2 ∈ X we have x1 ≤ φ (x2) if and only if f (x1) ≤ f (x2); (b) f is increasingly g–normal, for some function g of Y to X , if for any x ∈ X and y ∈ Y we have f (x) ≤ y if and only if...

For a new class of topological vector spaces, namely κ-normed spaces, an associated quasisemilinear topological preordered space is defined and investigated. This structure arise naturally from the consideration of a κ-norm, that is a distance function between a point and a G δ-subset. For it, analogs of the Hahn-Banach theorem are proved.

A partial order or poset   , P X   on a (finite) base set X determines the set   P  of linear extensions of P . The problem of computing, for a poset P , the cardinality of   P  is #P-complete. A set   1 2 , , , k P P P  of posets on X covers the set of linear orders that is the union of the   i P  . Given linear orders 1 2 , , , m L L L  on X , the Poset Cover problem is to de...

We obtain efficient conditions under which some or all solutions of a nonlinear equation in a topological vector space preordered by a closed wedge are comparable with respect to the corresponding preordering. Conditions sufficient for the equivalence of comparable solutions are also given. The wedge under consideration is not assumed to be a cone, nor any continuity conditions are imposed on t...