Mercredi 30 Août
Heure: 
11:00  12:30 
Lieu: 
Salle B107, bâtiment B, Université de Villetaneuse 
Résumé: 
Coherence for skew nearsemiring categories 
Description: 
Tarmo Uustalu We consider skew nearsemiring categories, a relaxation of nearsemiring categories where the unitors, associators, annihilator and distributor are not required to be natural isomorphisms, they are just natural transformations in a particular direction. We prove a coherence theorem for such categories. The theorem states that, in a free skew nearsemiring category over a set of objects, any two maps between an object and an object in normal form are equal.
Our main motivating examples for skew nearsemiring categories are from programming with effects. While (relative) monads and lax monoidal functors are the same as skew monoids in particular skew monoidal categories, (relative) MonadPlus and Alternative instances are skew nearsemiring objects.
This is joint work with Mauro Jaskelioff, Exequiel Rivas and Niccolò Veltri. 

