A calculus for four-valued sequential logic (Q549178)

In [``A propositional logic with 4 values: true, false, divergent and meaningless'', J. Appl. Non-Class. Log. 5, No. 2, 199--217 (1995; Zbl 0843.03012)], \textit{J. A. Bergstra, I. Bethke} and \textit{P. Rodenburg} introduced a four-valued logic to deal with the distinction between computation errors (e.g., divergence versus mistakes) in specification and programming. The current paper presents a complete finite equational axiomatisation of a sequential logic with four values based on that logic. Thereby ``sequential'' means that arguments are evaluated from left to right, until an answer is obtained.