 The equational theory of distributive lattices is obtained from that of Boolean algebras by selecting as its operations just the monotone binary operations on the two-element algebra, omitting the constants. These are the operations with the property that if either argument is changed from 0 to 1, the result does not change from 1 to 0. A distributive lattice is any model of those Boolean equations between terms built solely with monotone binary operations. Hence every Boolean algebra is a distributive lattice.