Complementary lemmas in the theory of binary relations

This paper presents a metatheorem with the following property: Given a proven axiom-free lemma, which interrelates some of the elementary properties of a binary relation, the metatheorem mechanically transforms this lemma into its uniquely corresponding complementary lemma. Therefore, the metatheorem nearly doubles our knowledge about the elementary properties of binary relations, for application to statistical decision theory. At present we do not know whether there exists a nontrivial axiom-free lemma that is its own complementary lemma.