Search arXiv⌕ Search
Home/Archive/arXiv

arXiv · math/0303323

What majority decisions are possible

Saharon Shelah
View original source ↗Read source document ↗Export metadata ↓

Abstract

The main result is the following: Let X be a finite set and D be a non empty family of choice functions for (X choose 2) closed under permutation of X. Then the following conditions are equivalent: (A) for any choice function c on (X choose 2) we can find a finite set J and c_j in D for j in J such that for any x not= y in X : c{x,y}=y Leftrightarrow |J|/2<| {j in J:c_j{x,y}= y}| (so equality never occurs) (B) for some c in D and x in X we have |{y: c{x,y}=y}| not= (|X|-1)/2 . We then describe what is the closure of a set of choice functions by majority; in fact, there are just two possibilities (in section 3). In section 4 we discuss a generalization.

Explore related subjects

math.COmath.LO

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Saharon Shelah. 2003-03-26. What majority decisions are possible. https://arxiv.org/abs/math/0303323

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

Rooted Spider Embeddings and the Erd\H os-Sós Conjecture

Under a local density condition, we prove that every $k$-edge spider embeds at any prescribed center of degree at least $k$, unless all legs are even and the host graph has one of two specified structures. These structures contain complete bipartite subgraphs with prescribed neighborhoods. The proof uses path rerouting and three exchange lemmas that describe equality in neighborhood estimates. As a consequence, we recover the Erd\H os-Sós bound for all spiders.

math.CO↗
arXiv2026

Generalized Goulden-Yong duals and signed minimal factorizations

In this paper, we give two combinatorial ways to study signed exceptional sequences. First, we show the equivalence between one-way reflections and relatively projective representations. Secondly, we construct generalized Goulden-Yong duals using reverse Garside element actions and folded chord diagrams. We then give two applications of the generalized Goulden-Yong duals: constructing generalized Prüfer codes and counting signed factorizations using the matrix-tree theorem.

math.CO↗
arXiv2026

Explicit expressions for iterates of power series

We present several formulas for both the discrete and fractional iterates of an invertible power series $f$, using a new unifying approach based on umbral calculus. Known formulas are extended, and their proofs simplified, while new expressions are introduced. In particular, by employing $q$-calculus identities, we eliminate the requirement for $f'(0)$ to equal $1$ and the resulting general expressions for the iterative logarithm are obtained as well.

math.CO↗