Vanderveken, D. i Nowak, M. 1993. An Algebraic Approach to a Concept of Proposition. Acta Universitatis Lodziensis. Folia Philosophica. Ethica-Aesthetica-Practica. 9 (sty. 1993), 115–123. DOI:https://doi.org/10.18778/0208-6107.09.12.