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## Über dieses Buch

Tamari lattices originated from weakenings or reinterpretations of the familar associativity law. This has been the subject of Dov Tamari's thesis at the Sorbonne in Paris in 1951 and the central theme of his subsequent mathematical work. Tamari lattices can be realized in terms of polytopes called associahedra, which in fact also appeared first in Tamari's thesis.

By now these beautiful structures have made their appearance in many different areas of pure and applied mathematics, such as algebra, combinatorics, computer science, category theory, geometry, topology, and also in physics. Their interdisciplinary nature provides much fascination and value.

On the occasion of Dov Tamari's centennial birthday, this book provides an introduction to topical research related to Tamari's work and ideas. Most of the articles collected in it are written in a way accessible to a wide audience of students and researchers in mathematics and mathematical physics and are accompanied by high quality illustrations.

## Inhaltsverzeichnis

### Dov Tamari (formerly Bernhard Teitler)

Abstract
The life of Dov Tamari is described, including a brief introduction to his mathematical work.
Folkert Müller-Hoissen, Hans-Otto Walther

### On Being a Student of Dov Tamari

Abstract
I reminisce about being a student of Dov Tamari at the State University of New York at Buffalo in the late 1960’s.
Carl Maxson

### How I ‘met’ Dov Tamari

Abstract
Although I never met Dov Tamari, neither in person nor electronically, our work had one important intersection – the associahedra. This Festschrift has given me the opportunity to set the record straight: the so-called Stasheff polytope was in fact constructed by Tamari in 1951, a full decade before my version. Here I will indulge in recollections of some of the history of the associahedra, its generalizations and applications. Others in this Festschrift will reveal still other aspects of Tamari’s vision, especially in more direct relation to the lattice/poset that bears his name.
Jim Stasheff

Without Abstract
Jean-Louis Loday

### Partial Groupoid Embeddings in Semigroups

Abstract
We examine a number of axiom systems guaranteeing the embedding of a partial groupoid into a semigroup. These include the Tamari symmetric partial groupoid and the Gensemer/Weinert equidivisible partial groupoid, provided they satisfy an additional axiom, weak associativity. Both structures share the one mountain property. More embedding results for partial groupoids into other types of algebraic structures are presented as well.
Susan H. Gensemer

### Moduli Spaces of Punctured Poincaré Disks

Abstract
The Tamari lattice and the associahedron provide methods of measuring associativity on a line. The real moduli space of marked curves captures the space of such associativity. We consider a natural generalization by considering the moduli space of marked particles on the Poincaré disk, extending Tamari’s notion of associativity based on nesting. A geometric and combinatorial construction of this space is provided, which appears in Kontsevich’s deformation quantization, Voronov’s swiss-cheese operad, and Kajiura and Stasheff’s open-closed string theory.

### Realizing the Associahedron: Mysteries and Questions

Abstract
There are many open problems and some mysteries connected to the realizations of the associahedra as convex polytopes. In this note, we describe three – concerning special realizations with the vertices on a sphere, the space of all possible realizations, and possible realizations of the multiassociahedron.
Cesar Ceballos, Günter M. Ziegler

### Permutahedra and Associahedra

Generalized associahedra from the geometry of finite reflection groups
Abstract
Permutahedra are a class of convex polytopes arising naturally from the study of finite reflection groups, while generalized associahedra are a class of polytopes indexed by finite reflection groups. We present the intimate links those two classes of polytopes share.
Christophe Hohlweg

### Combinatorial 2-truncated Cubes and Applications

Abstract
We study a class of simple polytopes, called 2-truncated cubes. These polytopes have remarkable properties and, in particular, satisfy Gal’s conjecture. Well-known polytopes (flag nestohedra, graph-associahedra and graph-cubeahedra) are 2-truncated cubes.
Victor M. Buchstaber, Vadim D. Volodin

### Extending the Tamari Lattice to Some Compositions of Species

Abstract
An extension of the Tamari lattice to the multiplihedra is discussed, along with projections to the composihedra and the Boolean lattice. The multiplihedra and composihedra are sequences of polytopes that arose in algebraic topology and category theory. Here we describe them in terms of the composition of combinatorial species. We define lattice structures on their vertices, indexed by painted trees, which are extensions of the Tamari lattice and projections of the weak order on the permutations. The projections from the weak order to the Tamari lattice and the Boolean lattice are shown to be different from the classical ones. We review how lattice structures often interact with the Hopf algebra structures, following Aguiar and Sottile who discovered the applications of Möbius inversion on the Tamari lattice to the Loday-Ronco Hopf algebra.
Stefan Forcey

### Tamari Lattices and the Symmetric Thompson Monoid

Abstract
We investigate the connection between Tamari lattices and the Thompson group F, summarized in the fact that F is a group of fractions for a certain monoid $${F^+_{\rm sym}}$$whose Cayley graph includes all Tamari lattices. Under this correspondence, the Tamari lattice meet and join are the counterparts of the least common multiple and greatest common divisor operations in $${F^+_{\rm sym}}$$. As an application, we show that, for every n, there exists a length l chain in the nth Tamari lattice whose endpoints are at distance at most 12l/n.
Patrick Dehornoy

### Parenthetic Remarks

Abstract
The Tamari lattice provides an example of a (non-symmetric) operad. We discuss such operads and their associated monads and monoidal categories. Freeness is an important aspect. The free structures are described in various ways using wellformed words (in the spirit of some of Tamari’s papers), using string diagrams leading to forests, and in terms of rewrite rules.
Ross Street

### On the Categories of Modules Over the Tamari Posets

Abstract
One can attach an Abelian category to each Tamari poset, the category of modules over its incidence algebra. This can also be described as the category of modules over the Hasse diagram of the poset, seen as a quiver with relations. The derived category of this category seems to be a very interesting object, with nice properties and many different descriptions.We recall known results and present some conjectures on these derived categories.
Frédéric Chapoton

### The Tamari Lattice as it Arises in Quiver Representations

Abstract
In this chapter, we explain how the Tamari lattice arises in the context of the representation theory of quivers, as the poset whose elements are the torsion classes of a directed path quiver, with the order relation given by inclusion.
Hugh Thomas

### From the Tamari Lattice to Cambrian Lattices and Beyond

Abstract
We trace the path from the Tamari lattice, via lattice congruences of the weak order, to the definition of Cambrian lattices in the context of finite Coxeter groups, and onward to the construction of Cambrian fans. We then present sortable elements, the key combinatorial tool for studying Cambrian lattices and fans. The chapter concludes with a brief description of the applications of Cambrian lattices and sortable elements to Coxeter-Catalan combinatorics and to cluster algebras.

### Catalan Lattices on Series Parallel Interval Orders

Abstract
Using the notion of series parallel interval order, we propose a unified setting to describe Dyck lattices and Tamari lattices (two well-known lattice structures on Catalan objects) in terms of basic notions of the theory of posets. As a consequence of our approach, we find an extremely simple proof of the fact that the Dyck order is a refinement of the Tamari one. Moreover, we provide a description of both the weak and the strong Bruhat order on 312-avoiding permutations, by recovering the proof of the fact that they are isomorphic to the Tamari and the Dyck order, respectively; our proof, which simplifies the existing ones, relies on our results on series parallel interval orders.
Filippo Disanto, Luca Ferrari, Renzo Pinzani, Simone Rinaldi

### Generalized Tamari Order

Abstract
In [2], M. Carr and S. Devadoss introduced the notion of tubing on a finite simple graph G. When G is the linear graph Ln, with n vertices, the polytope K Ln is the Stasheff polytope or associahedron. Our goal is to describe a partial order on the set of tubings of a simple graph, which generalizes the Tamari order on the set of vertices of the associahedron. For certain families of graphs, this order induces an associative product on the vector space spanned by the tubings of all the graphs.
María Ronco

### A Survey of the Higher Stasheff-Tamari Orders

Abstract
The Tamari lattice, thought as a poset on the set of triangulations of a convex polygon with n vertices, generalizes to the higher Stasheff-Tamari orders on the set of triangulations of a cyclic d-dimensional polytope having n vertices. This survey discusses what is known about these orders, and what one would like to know about them.
Jörg Rambau, Victor Reiner

### KP Solitons, Higher Bruhat and Tamari Orders

Abstract
In a tropical approximation, any tree-shaped line soliton solution, a member of the simplest class of soliton solutions of the Kadomtsev-Petviashvili (KP-II) equation, determines a chain of planar rooted binary trees, connected by right rotation. More precisely, it determines a maximal chain of a Tamari lattice. We show that an analysis of these solutions naturally involves higher Bruhat and higher Tamari orders.
Aristophanes Dimakis, Folkert Müller-Hoissen

### Backmatter

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