  Leśniewski’s preference for an axiom system, based in part on the success of Ontology, and also on considerations about the nature of definition, was to base a logical system on the single connective of material equivalence, together with the universal quantifier. He was held up for some time in doing this for Protothetic by his inability to see how to eliminate the connective of conjunction in terms of equivalence. Given quantification and equivalence, negation is easy to define, in a way Russell once suggested to Frege: