Dendroidal sets

Ieke Moerdijk*, Ittay Weiss

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


We introduce the concept of a dendroidal set. This is a generalization of the notion of a simplicial set, specially suited to the study of (coloured) operads in the context of homotopy theory. We define a category of trees, which extends the category δ used in simplicial sets, whose presheaf category is the category of dendroidal sets. We show that there is a closed monoidal structure on dendroidal sets which is closely related to the Boardman-Vogt tensor product of (coloured) operads. Furthermore, we show that each (coloured) operad in a suitable model category has a coherent homotopy nerve which is a dendroidal set, extending another construction of Boardman and Vogt. We also define a notion of an inner Kan dendroidal set, which is closely related to simplicial Kan complexes. Finally, we briefly indicate the theory of dendroidal objects in more general monoidal categories, and outline several of the applications and further theory of dendroidal sets.

Original languageEnglish
Pages (from-to)1441-1470
Number of pages30
JournalAlgebraic and Geometric Topology
Issue number1
Publication statusPublished - 2007


  • Algebras up to homotopy
  • Homotopy coherent nerve
  • Kan complex
  • Operad
  • Tensor product of operads
  • Weak n-categories


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