Polynomial Functors and Trees

By Joachim Kock. 2008

78 citations recorded by the source corpus.

We explore the relationship between polynomial functors and trees. In the first part we characterise trees as certain polynomial functors and obtain a completely formal but at the same time conceptual and explicit construction of two categories of rooted trees, whose main properties we describe in terms of some factorisation systems. The second category is the category Ω of Moerdijk and Weiss. Although the constructions are motivated and explained in terms of polynomial functors, they all amount to elementary manipulations with finite sets. Included in Part 1 is also an explicit construction of the free monad on a polynomial endofunctor, given in terms of trees. In the second part we describe polynomial endofunctors and monads as structures built from trees, characterising the images of several nerve functors from polynomial endofunctors and monads into presheaves on categories of trees. Polynomial endofunctors and monads over a base are characterised by a sheaf condition on categories of decorated trees. In the absolute case, one further condition is needed, a projectivity condition, which serves also to characterise polynomial endofunctors and monads among (coloured) collections and operads.

Subfields: Geometry and Topology, Mathematical Physics, Molecular Biology

View Paper: https://www.semanticscholar.org/paper/221b9d3b14c85884db02f94a7a1bbb90db3f0c21

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Citations in the corpus

Polynomial functors and polynomial monads (2009, methodology): “This paper was conceived in parallel to [35, 36], to take care of foundational issues.”
Decomposition spaces, incidence algebras and Möbius inversion I: Basic theory (2015, background): “Other important instances of generic-free factorisation systems are found in the category of rooted trees [42] (where the monad is the free-operad monad), the category of Feynman graphs [38] (where the monad is the free-modular-operad monad), the category of directed graphs [46] (where the monad is ”
Monads with arities and their associated theories (2011, unknown): “[34, section 2] or the work of Kock [19] and Joyal–Kock [17].”
Homotopy theory for algebras over polynomial monads (2013, unknown): “[38] An I-coloured bouquet of arity k is a polynomial I ✛ s {1, 2, .”