  Leśniewski’s systems have some formal features, even very peculiar ones in some respects. All are axiomatic. According to his nominalistic preferences, they are concrete physical objects. Expressions are always understood as sequences of concrete inscriptions. There are as many expressions as have been written; no expression exists merely potentially. This view is called constructive nominalism. According to it, two intuitively equivalent systems, for example, protothetic based on equivalence and protothetic based on implication, are different systems. Every logical system, on Leśniewski’s view, is not finished at any time because there is always the possibility of adding new elements to it. Hence, the rules for constructing and developing formal systems are of crucial importance for Leśniewski’s logics. He understood this very well and devoted much attention to explaining the details of his formalization. Leśniewski formulated his procedural directives purely syntactically and completely. Due to the role of equivalence, he was able to treat definitions as theorems. In general, Leśniewski’s systems are commonly considered to be perfect from the point of view of the requirements of correct formalization. The Leśniewski project is a version of logicism. Leśniewski’s three systems form a grand logic and provide a universal language to capture the whole of knowledge. It is certainly not an orthodox system and lies on the margin of contemporary research in logic. Yet it continues to attract many logicians and philosophers. In spite of their marginality, Leśniewski’s systems are investigated in all parts of the world.