An algebraic theory of normal forms (Q1346245)

Based on \textit{E. J. Dubuc's} [J. Algebra 29, 208-228 (1974; Zbl 0291.18010)] free monoid construction, the author gives a general theory of normal forms, which is then applied to propositional modal logics. The author's conception of normal forms as labelled trees and forests was already implicit in \textit{K. Fine's} paper [Notre Dame J. Formal Logic 16, 229-237 (1975; Zbl 0298.02015)]. The prerequisites are minimal; the reader is only required to be familiar with the standard techniques of algebraic logic and the basic facts about adjoint functors.