The notion of a subtractive category, recently introduced by the author, is a “categorical version” of the notion of a (pointed) subtractive variety of universal algebras, due to A.Ursini. We show that a subtractive variety C, whose theory contains a unique constant, is abelian (i.e. C is the variety of modules over a fixed ring), if and only if the dual category Cop of C, is subtractive. More ...

The purpose of this paper is to study some obstruction classes induced by a construction homotopy-theoretic version projective TQFT (projective HTQFT for short). A given symmetric monoidal functor whose domain the cospan category pointed finite CW-spaces instead cobordism category. We construct pair HTQFT’s starting from [Formula: see text]-valued Brown where text] bicommutative Hopf algebras o...