The sentential calculus using rule of inference Re
R. B. Angell · Journal of Symbolic Logic · 1960
Axiomatizations of the sentential calculus which use Rmp (modus ponens), have been shown equivalent to axiomatizations similar in all respects except that Rmp is replaced by the less restricted rule Re (rule of excision)1: Re. If S and (…(S⊃S') …), then (… S' …).