a necessary and sufficient condition in terms of lower cut sets are given for the insertion of a $gamma-$continuous function between two comparable real-valued functions.

This paper is a survey on SPG-reguli, SPG-systems, BLT-sets and sets with the BLT-property. It is shown how from these sets generalized quadrangles, partial geometries and semi-partial geometries can be constructed. Many examples are given and open problems are stated. There are also some new results. c © 2007 Elsevier B.V. All rights reserved.

A coordinate cone in R n is an intersection of some coordinate hy-perplanes and open coordinate half-spaces. A semi-monotone set is an open bounded subset of R n , definable in an o-minimal structure over the reals, such that its intersection with any translation of any coordinate cone is connected. This can be viewed as a generalization of the convexity property. Semi-monotone sets have a numb...

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It is a truism that all of mathematics can be expressed in the language of set theory, i.e. the predicate calculus (including equality) with the single two-place relation ∈. As with any other countable language, the language of set theory is subject to the Löwenheim-Skolem Theorem, which asserts that if we have some axioms – e.g. the usual axioms of set theory (ZFC) – formulated in this languag...