D. Cantone et Mn. Asmundo, A further and effective liberalization of the delta-rule in free variable semantic tableaux, LECT N A I, 1761, 2000, pp. 109-125
In this paper, we present a further liberalization of the delta -rule in fr
ee variable semantic tableaux. It is effective in that (1) it is both a nat
ural and intuitive liberalization, and (2) can reduce the proof size non el
ementarily as compared to previous versions of the delta -rule.