Graded algebras and subproduct systems: dimension two

Abstract

Objects dual to graded algebras are subproduct systems of linear spaces, a purely algebraic counterpart of a notion introduced recently in the context of noncommutative dynamics (Shalit and Solel, Bhat and Mukherjee). A complete classification of these objects in the lowest nontrivial dimension is given in this work, triggered by a question of Bhat.