On co-Filters in Semigroups with Apartness

The logical environment of this research is the Intuitionistic Logic and principled-philosophical orientation of the Bishop’s Constructive Mathematics. In this paper, basing our consideration on the sets with the apartness relation, we analyze the lattices of all co-filters of an ordered semigroup under a co-quasiorder as a continuation of our article [?]. We prove a number of results related to co-filters in a semigroup with apartness and the lattice of all co-filters of such semigroups.

Free Logics are Cut-Free

The paper presents a uniform proof-theoretic treatment of several kinds of free logic, including the logics of existence and definedness applied in constructive mathematics and computer science, and called here quasi-free logics. All free and quasi-free logics considered are formalised in the framework of sequent calculus, the latter for the first time. It is shown that in all cases remarkable simplifications of the starting systems are possible due to the special rule dealing with identity and existence predicate. Cut elimination is proved in a constructive way for sequent calculi adequate for all logics under consideration.

Conceptions of Infinity and Set in Lorenzen’s Operationist System

In the late 1940s and early 1950s, Lorenzen developed his operative logic and mathematics, a form of constructive mathematics. Nowadays this is mostly seen as a precursor of the better-known dialogical logic (Notable exceptions are the works of Schroeder-Heister 2008; Coquand and Neuwirth 2017; Kahle and Oitavem 2020.), and one might assume that the same philosophical motivations were present in both works. However, we want to show that this is not everywhere the case. In particular, we claim that Lorenzen’s well-known rejection of the actual infinite, as stated in Lorenzen (1957), was not a major motivation for operative logic and mathematics. Rather, we argue that a shift happened in Lorenzen’s treatment of the infinite from the early to the late 1950s. His early motivation for the development of operationism is concerned with a critique of the Cantorian notion of set and with related questions about the notions of countability and uncountability; it is only later that his motivation switches to focusing on the concept of infinity and the debate about actual and potential infinity.

Lorenzen and Constructive Mathematics

The goal of this paper is to present a short survey of some of Lorenzen’s contributions to constructive mathematics, and its influence on recent developments in mathematical logic and constructive algebra. We also present some work in measure theory which uses these contributions in an essential way.

Can we preserve physically meaningful “macro” analyticity without requiring physically meaningless “micro” analyticity?

Physicists working on quantum field theory actively used “macro” analyticity — e.g., that an integral of an analytical function over a large closed loop is 0 — but they agree that “micro” analyticity — the possibility to expand into Taylor series — is not physically meaningful on the micro level. Many physicists prefer physical theories with physically meaningful mathematical foundations. So, a natural question is: can we preserve physically meaningful “macro” analyticity without requiring physically meaningless “micro” analyticity? In the 1970s, an attempt to do it was made by using constructive mathematics, in which only objects generated by algorithms are allowed. This did not work out, but, as we show in this paper, the desired separation between “macro” and “micro” analyticity can be achieved if we limit ourselves to feasible algorithms.