The M\"obius function of the consecutive pattern poset

An occurrence of a consecutive permutation pattern $p$ in a permutation $\pi$ is a segment of consecutive letters of $\pi$ whose values appear in the same order of size as the letters in $p$. The set of all permutations forms a poset with respect to such pattern containment. We compute the M\"obius function of intervals in this poset, providing what may be called a complete solution to the problem. For most intervals our results give an immediate answer to the question. In the remaining cases, we give a polynomial time algorithm to compute the M\"obius function. In particular, we show that the M\"obius function only takes the values -1, 0 and 1.Comment: 10 pages, 2 figure

Restricted binary strings and generalized Fibonacci numbers

Part 2: Regular PapersInternational audienceWe provide some interesting relations involving k-generalized Fibonacci numbers between the set $F_n^{(k)}$ of length n binary strings avoiding k of consecutive 0’s and the set of length n strings avoiding $k+1$ consecutive 0’s and 1’s with some more restriction on the first and last letter, via a simple bijection. In the special case $k=2$ a probably new interpretation of Fibonacci numbers is given.Moreover, we describe in a combinatorial way the relation between the strings of $F_n^{(k)}$ with an odd numbers of 1’s and the ones with an even number of 1’s

Vincular pattern posets and the M\"obius function of the quasi-consecutive pattern poset

We introduce vincular pattern posets, then we consider in particular the quasi-consecutive pattern poset, which is defined by declaring $\sigma \leq \tau$ whenever the permutation $\tau$ contains an occurrence of the permutation $\sigma$ in which all the entries are adjacent in $\tau$ except at most the first and the second. We investigate the M\"obius function of the quasi-consecutive pattern poset and we completely determine it for those intervals $[\sigma ,\tau ]$ such that $\sigma$ occurs precisely once in $\tau$.Comment: 13 pages, 4 figure