© The London Mathematical Society
Asymptotic Enumeration and Logical Limit Laws for Expansive Multisets and Selections
Department of Mathematics, Technion-Israel Institute of Technology Haifa 32000, Israel mar18aa{at}techunix.technion.ac.i
School of Mathematical Sciences, Queen Mary, University of London London E1 4NS, United Kingdom D.S.Stark{at}maths.qmul.ac.uk
Received 16 July 2004. Revision received 25 February 2005.
Given a sequence of integers aj, j
1, a multiset is a combinatorial object composed of unordered components, such that there are exactly aj one-component multisets of size j. When aj
jr1 yj for some r > 0, y
1, then the multiset is called expansive. Let cn be the number of multisets of total size n. Using a probabilistic approach, we prove for expansive multisets that cn/cn+1
1 and that cn/cn+1 < 1 for large enough n. This allows us to prove monadic second-order limit laws for expansive multisets. The above results are extended to a class of expansive multisets with oscillation.
Moreover, under the condition aj = Kjr1 yj + O(y
j), where K > 0, r > 0, y > 1,
(0, 1), we find an explicit asymptotic formula for cn. In a similar way we study the asymptotic behavior of selections, which are defined as combinatorial objects composed of unordered components of distinct sizes.