A new view of effects in a Hilbert space

We investigate certain Brouwer-Zadeh lattices that serve as abstract counterparts of lattices of e¤ects in Hilbert spaces under the spectral ordering. These algebras, called PBZ*-lattices, can also be seen as generalisations of orthomodular lattices and are remarkable for the collapse of three notions of “sharpness”that are distinct in general Brouwer-Zadeh lattices. We investigate the structure theory of PBZ*- lattices and their reducts; in particular, we prove some embedding re- sults for PBZ*-lattices and provide an initial description of the lattice of PBZ*-varieties.