Sequential products in effect categories

A new categorical framework is provided for dealing with multiple argu- ments in a programming language with effects, for example in a language withimperativefeatures. Likerelatedframeworks(Monads,Arrows,Freyd categories), we distinguishtwo kinds offunctions. In addition, we also dis- tinguish two kinds of equations. Then, we are able to define a kind of product, that generalizes the usual categorical product. This yields a pow- erful tool for deriving many results about languages with effects.