  It is shown that operations of equivalence cannot serve for building algebras
which would induce orthomodular lattices as the operations of implication can.
Several properties of equivalence operations have been investigated.
Distributivity of equivalence terms and several other 3 variable expressions
involving equivalence terms have been proved to hold in any orthomodular
lattice. Symmetric differences have been shown to reduce to complements of
equivalence terms. Some congruence relations related to equivalence operations
and symmetric differences have been considered.
