 Peirce also broke with Boole’s and Jevons’ use of equality as the fundamental primitive, using instead the relation of “subsumption” interpretable in different ways (subclass relation, implication, etc.). He stated the partial order properties of subsumption and then proceeded to define the operations of + and × as least upper bounds and greatest lower bounds—he implicitly assumed such bounds existed—and listed the key equational properties of the algebras with two binary operations that we now call lattices. Then he claimed that the distributive law followed, but said the proof was too tedious to include. The fruitfulness of this perspective is evident in his seminal paper from 1885. There Peirce introduced a system for propositional logic based on five axioms for implication (represented by the sign ‘\(-\kern-.4em&lt;\)’), including what is now called Peirce’s law. It certainly made the algebra of logic more elegant.