Two binary operations, ¤ and ⁂, are said to be connected by the absorption law if: A set equipped with two commutative and associative binary operations
("meet") that are connected by the absorption law is called a lattice; in this case, both operations are necessarily idempotent (i.e. a
In classical logic, and in particular Boolean algebra, the operations OR and AND, which are also denoted by
, satisfy the lattice axioms, including the absorption law.
In the last case, there is no one-to-one correspondence between the free variables of the defining pair of identities.