TY - JOUR

T1 - Triangulations, orientals, and skew monoidal categories

AU - Lack, Stephen

AU - Street, Ross

PY - 2014/6/20

Y1 - 2014/6/20

N2 - A concrete model of the free skew-monoidal category Fsk on a single generating object is obtained. The situation is clubbable in the sense of G.M. Kelly, so this allows a description of the free skew-monoidal category on any category. As the objects of Fsk are meaningfully bracketed words in the skew unit I and the generating object X, it is necessary to examine bracketings and to find the appropriate kinds of morphisms between them. This leads us to relationships between triangulations of polygons, the Tamari lattice, left and right bracketing functions, and the orientals. A consequence of our description of Fsk is a coherence theorem asserting the existence of a strictly structure-preserving faithful functor Fskδ ⊥ where δ ⊥ is the skew-monoidal category of finite non-empty ordinals and first-element-and-order-preserving functions. This in turn provides a complete solution to the word problem for skew monoidal categories.

AB - A concrete model of the free skew-monoidal category Fsk on a single generating object is obtained. The situation is clubbable in the sense of G.M. Kelly, so this allows a description of the free skew-monoidal category on any category. As the objects of Fsk are meaningfully bracketed words in the skew unit I and the generating object X, it is necessary to examine bracketings and to find the appropriate kinds of morphisms between them. This leads us to relationships between triangulations of polygons, the Tamari lattice, left and right bracketing functions, and the orientals. A consequence of our description of Fsk is a coherence theorem asserting the existence of a strictly structure-preserving faithful functor Fskδ ⊥ where δ ⊥ is the skew-monoidal category of finite non-empty ordinals and first-element-and-order-preserving functions. This in turn provides a complete solution to the word problem for skew monoidal categories.

UR - http://www.scopus.com/inward/record.url?scp=84896968960&partnerID=8YFLogxK

U2 - 10.1016/j.aim.2014.03.003

DO - 10.1016/j.aim.2014.03.003

M3 - Article

VL - 258

SP - 351

EP - 396

JO - Advances in Mathematics

JF - Advances in Mathematics

SN - 0001-8708

ER -