  Although various schemes for anhomomorphic logics for quantum mechanics have
been considered in the past we shall mainly concentrate on the quadratic or
grade-2 scheme. In this scheme, the grade-2 truth functions are called
coevents. We discuss properties of coevents, projections on the space of
coevents and the master observable. We show that the set of projections forms
an orthomodular poset. We introduce the concept of precluding coevents and show
that this is stronger than the previously studied concept of preclusive
coevents. Precluding coevents are defined naturally in terms of the master
observable. A result that exhibits a duality between preclusive and precluding
coevents is given. Some simple examples are presented.
