On natural join of posets properties and first applications

Abstract

In addition to the three standard operations on posets which are dual of poset or ordinal and cardinal sums of partial ordered sets one adds the natural join of posets. This is especially natural natural join operation for graded posets including very special and important the so called cobweb posets. The main aims of this article are the presentation of the authors update applications of natural join of posets in the domain of graded posets and summary of the general properties of natural join of posets with posing some questions arising on the way. Thus in this note apart from revealing some general properties of natural join of posets we also deliver the authors combinatorial interpretations of cobweb posets including discrete hyperboxes coding of the so called cobweb posets .Various explicit formulas for the zeta functions and zeta matrices as well as the inverse of zeta matrix for any graded posets are supplied. Whitney numbers formulas and those for characteristic polynomials are given too.

34 pages 16 figures The Internet Gian-Carlo Rota Polish Seminar article http://ii.uwb.edu.pl/akk/sem/sem\_rota.htm

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