A propositional logic with 4 values: true, false, divergent and meaningless
Jan Aldert Bergstra, Inge Bethke, Piet H. Rodenburg · Journal of Applied Non-Classical Logics · 1995
In this paper, we survey 3-valued logics and their complete axiomatizations, one of which may be new. We then propose a 4-valued, functionally complete logic that incorporates these 3-valued systems and provide notations for interesting operators and subsystems.