Pita factorisation in operadic categories

Abstract: In strictly factorisable operadic categories, every morphism $f$ factors uniquely as $f=η_f \circ π_f$ where $η_f$ is order-preserving and $π_f$ is a quasi-bijection that is order-preserving on the fibres of $η_f$. We call it the pita factorisation. In this paper we develop some general theory to compensate for the fact that generally pita factorisations do not form an orthogonal factorisation system. The main technical result states that a certain simplicial object in Cat, called the pita nerve, is oplax (rather than strict as it would be for an orthogonal factorisation system). The main application is the result that the so-called operadic nerve of any operadic category is coherent. This result is a key ingredient in the simplicial approach to operadic categories developed in the `main paper' \cite{Batanin-Kock-Weber:mainpaper}, which motivated the present paper. We also show that in the important case where quasibijections are invertible, the pita nerve is a decomposition space.