 It was Arthur Prior who, in 1956, first proved that BF is a theorem of SQML (without identity). Clearly aware of its possibilist and necessitist implications, Prior sought to develop a logic consistent with strict actualism and, hence, a logic in which BF, CBF, and \(\Box\textbf{N}\) all fail. The result was his deductive system Q. The first installment—the propositional component (Prior 1957: chs. IV and  V[74])—arrived  only a year later; quantification theory with identity was added a decade later (Prior 1968b, 1968c).