Call an orthomodular lattice LM-symmetric if M(e,f) implies M(f,e) for all e,f ∈ L and O-symmetric if M(e,f)
implies M(f′,e′). To check for these properties it is sufficient to consider only those
modular pairs in which the two elements are complements. Every O-symmetric lattice
is M-symmetric. In an atomic orthomodular lattice, M-symmetry is equivalent to the
atomic exchange property.