  The easiest way to get an idea of how definitions work in Leśniewski’s logic is not to look at the published work on Mereology or Protothetic, but at the extended list of “Definitions and Theses of Leśniewski’s Ontology” from S. Leśniewski’s Lecture Notes on Logic, published in 1988. Taken from student notes of a 1929–30 lecture course ‘Elementary Outline of Ontology’, they comprise one axiom, 59 definitions and 633 listed (not proved) theorems, covering syllogistic, Boolean algebra, the notions of property(-predicate) and higher-order property, relations, higher-order epsilons, and several chunks of the theory of relations including converses, fields and relative products, as known from Peirce, Schröder, Whitehead and Russell. Not coincidentally, the sketched development includes a large number of styles of parentheses.