The Open University of Japan

Explicit Two-Variable Bases and the Single-Equation Problem for iEx-Logic

We study Ex-algebras, which capture the common sequent validities of Heyting algebras and orthomodular algebras with Sasaki implication. Over the fixed fundamental-algebra base in the original signature {meet, join, implication, 0, 1}, we prove a two-local representation theorem...

Characterization of Vitamin B12 Levels and Compounds in Commercial and Homemade Kombucha

Abstract Vitamin B12 is an essential nutrient produced only by certain bacteria and archaea. Kombucha has been promoted as a plant-based source of vitamin B12 to overcome the risk of deficiency associated with vegetarian diets. In this study, the vitamin B12 content of commercial...

A countable three-generated orthomodular lattice with no σ-complete embedding

We construct a countably infinite orthomodular lattice generated by three specified elements that has no bounded ortholattice embedding into any set-sized σ-complete orthomodular lattice. In particular, it has no embedding into any set-sized complete orthomodular lattice. The exa...

Rational functions that satisfy fn + gn + hn = 1

Solutions of non-constant rational functions of the Fermat type functional equations ( ⁎ ) f n + g n + h n = 1 , where n ≥ 2 are integers, are considered in the complex plane. It is known that ( ⁎ ) cannot possess non-constant rational function solutions when n ≥ 8 , and that the...

Enhancing Marine Fuel Supply Chain Resilience: A Comparative Study of Lagos Waters and Singapore

Offshore marine fuel supply chains represent a critical operational intersection between maritime logistics, commercial energy trading and national regulatory enforcement. However, vulnerability to quantity discrepancies, operational opacity and jurisdictional fragmentation conti...