Every presheaf (let's say on a topological space) comes with restriction maps. The open sets of a topological space are ordered by inclusion and these inclusions yield the restrictions. Now a sheaf satisfies a gluing condition: that you can glue along elements which coincide on common restrictions. Every simplicial object (let's say a simplicial set) comes with face maps. The simplex category is ordered by faces & degeneracies and these maps yield simplicial maps. Now a Kan complex satisfies a gluing condition: that you can glue along simplices which coincide on common faces. Is there a deeper theoretical framework to relate these 2 notions? I guess that this is the case, and that it is rather trivial. Side-question: Can we define "degeneracies" for presheaves? Ideas?