  Similarity-Projection structures abstract the numerical properties of real
scalar product of rays and projections in Hilbert spaces to provide a more
general framework for Quantum Physics. They are characterized by properties
that possess direct physical meaning. They provide a formal framework that
subsumes both classical boolean logic concerned with sets and subsets and
quantum logic concerned with Hilbert space, closed subspaces and projections.
They shed light on the role of the phase factors that are central to Quantum
Physics. The generalization of the notion of a self-adjoint operator to
SP-structures provides a novel notion that is free of linear algebra.

Quantum Physics