What year introduced the free substitution rule? [SEP] There were also several rule changes in this period.
entailment not_entailment entailment not_entailment entailment not_entailment not_entailment entailment not_entailment entailment entailment entailment entailment entailment not_entailment entailment entailment not_entailment not_entailment entailment not_entailment not_entailment not_entailment entailment not_entailment entailment entailment entailment not_entailment not_entailment entailment not_entailment not_entailment not_entailment not_entailment entailment entailment not_entailment entailment entailment not_entailment entailment entailment not_entailment entailment not_entailment entailment not_entailment not_entailment not_entailment entailment entailment entailment not_entailment entailment entailment not_entailment entailment not_entailment not_entailment entailment not_entailment not_entailment not_entailment not_entailment not_entailment not_entailment entailment not_entailment entailment not_entailment entailment not_entailment entailment not_entailment entailment entailment entailment not_entailment not_entailment not_entailment entailment entailment entailment not_entailment not_entailment not_entailment not_entailment entailment not_entailment not_entailment entailment entailment entailment entailment entailment entailment not_entailment entailment entailment not_entailment not_entailment not_entailment not_entailment not_entailment entailment entailment not_entailment entailment entailment entailment entailment entailment entailment not_entailment entailment not_entailment not_entailment not_entailment not_entailment not_entailment entailment entailment entailment entailment entailment entailment not_entailment entailment entailment entailment not_entailment not_entailment entailment not_entailment not_entailment entailment not_entailment not_entailment not_entailment entailment not_entailment entailment entailment not_entailment entailment not_entailment not_entailment not_entailment not_entailment not_entailment not_entailment entailment not_entailment not_entailment not_entailment not_entailment entailment entailment entailment entailment not_entailment not_entailment entailment not_entailment entailment not_entailment entailment not_entailment entailment not_entailment not_entailment not_entailment entailment not_entailment entailment entailment not_entailment not_entailment not_entailment entailment not_entailment entailment entailment not_entailment not_entailment not_entailment not_entailment not_entailment entailment not_entailment entailment entailment entailment entailment not_entailment entailment entailment entailment not_entailment entailment entailment not_entailment entailment not_entailment entailment entailment not_entailment not_entailment not_entailment not_entailment not_entailment not_entailment entailment not_entailment not_entailment not_entailment not_entailment not_entailment not_entailment not_entailment entailment not_entailment not_entailment entailment entailment not_entailment not_entailment not_entailment entailment not_entailment entailment entailment entailment not_entailment entailment entailment not_entailment entailment not_entailment not_entailment entailment entailment not_entailment not_entailment not_entailment not_entailment entailment not_entailment entailment entailment entailment not_entailment not_entailment entailment not_entailment not_entailment entailment entailment entailment entailment entailment not_entailment not_entailment not_entailment entailment not_entailment not_entailment entailment entailment entailment not_entailment entailment entailment entailment not_entailment not_entailment not_entailment entailment entailment entailment not_entailment entailment not_entailment entailment entailment not_entailment not_entailment entailment entailment not_entailment entailment not_entailment entailment entailment not_entailment entailment entailment entailment not_entailment entailment entailment entailment entailment not_entailment entailment not_entailment entailment not_entailment entailment entailment not_entailment entailment entailment entailment not_entailment not_entailment entailment entailment entailment not_entailment not_entailment entailment not_entailment not_entailment entailment not_entailment not_entailment entailment entailment entailment entailment not_entailment not_entailment not_entailment not_entailment not_entailment entailment entailment not_entailment not_entailment not_entailment entailment entailment entailment not_entailment entailment entailment entailment entailment entailment not_entailment not_entailment not_entailment entailment not_entailment entailment not_entailment entailment not_entailment not_entailment not_entailment entailment not_entailment entailment not_entailment not_entailment not_entailment entailment entailment not_entailment not_entailment entailment not_entailment not_entailment not_entailment entailment not_entailment not_entailment not_entailment not_entailment not_entailment not_entailment not_entailment entailment not_entailment not_entailment not_entailment not_entailment not_entailment entailment entailment not_entailment entailment not_entailment entailment not_entailment entailment not_entailment not_entailment entailment entailment entailment entailment not_entailment entailment entailment not_entailment not_entailment not_entailment entailment not_entailment entailment not_entailment not_entailment not_entailment not_entailment not_entailment not_entailment entailment not_entailment not_entailment entailment not_entailment not_entailment not_entailment not_entailment not_entailment not_entailment not_entailment not_entailment not_entailment not_entailment not_entailment not_entailment entailment not_entailment entailment not_entailment not_entailment entailment entailment entailment entailment not_entailment not_entailment entailment entailment not_entailment entailment entailment entailment not_entailment not_entailment not_entailment entailment not_entailment not_entailment not_entailment not_entailment not_entailment not_entailment entailment entailment entailment not_entailment entailment entailment entailment not_entailment entailment not_entailment not_entailment entailment not_entailment not_entailment entailment entailment entailment not_entailment entailment not_entailment entailment entailment entailment not_entailment not_entailment entailment entailment entailment entailment not_entailment entailment not_entailment entailment not_entailment entailment not_entailment not_entailment entailment not_entailment not_entailment not_entailment entailment entailment not_entailment not_entailment not_entailment entailment entailment not_entailment entailment entailment entailment not_entailment entailment not_entailment not_entailment entailment not_entailment entailment entailment not_entailment not_entailment not_entailment not_entailment entailment not_entailment not_entailment entailment entailment not_entailment entailment not_entailment not_entailment not_entailment not_entailment entailment entailment not_entailment not_entailment not_entailment entailment not_entailment not_entailment entailment entailment entailment not_entailment not_entailment entailment entailment not_entailment entailment not_entailment not_entailment entailment entailment entailment entailment not_entailment entailment not_entailment not_entailment not_entailment not_entailment not_entailment entailment entailment not_entailment not_entailment not_entailment not_entailment not_entailment not_entailment entailment not_entailment entailment entailment not_entailment not_entailment not_entailment not_entailment entailment entailment entailment not_entailment entailment entailment not_entailment entailment not_entailment entailment not_entailment not_entailment entailment entailment not_entailment entailment not_entailment not_entailment entailment not_entailment entailment entailment not_entailment entailment not_entailment entailment entailment not_entailment not_entailment not_entailment not_entailment entailment not_entailment entailment entailment not_entailment not_entailment not_entailment entailment entailment not_entailment entailment not_entailment entailment entailment not_entailment not_entailment not_entailment entailment entailment entailment entailment not_entailment entailment not_entailment entailment not_entailment entailment not_entailment entailment not_entailment entailment not_entailment entailment not_entailment entailment entailment entailment not_entailment not_entailment entailment not_entailment not_entailment entailment not_entailment not_entailment not_entailment not_entailment entailment not_entailment entailment not_entailment not_entailment entailment entailment not_entailment not_entailment entailment entailment entailment entailment entailment entailment not_entailment not_entailment not_entailment not_entailment entailment not_entailment not_entailment not_entailment not_entailment entailment not_entailment not_entailment not_entailment entailment not_entailment not_entailment entailment not_entailment entailment entailment entailment not_entailment entailment entailment not_entailment entailment not_entailment entailment not_entailment not_entailment entailment entailment not_entailment entailment not_entailment entailment entailment entailment entailment not_entailment entailment not_entailment not_entailment entailment entailment not_entailment entailment entailment entailment not_entailment not_entailment entailment not_entailment not_entailment not_entailment entailment entailment entailment not_entailment entailment not_entailment not_entailment not_entailment not_entailment entailment not_entailment entailment not_entailment not_entailment not_entailment not_entailment not_entailment not_entailment not_entailment not_entailment not_entailment not_entailment entailment not_entailment entailment entailment entailment entailment not_entailment not_entailment not_entailment entailment entailment entailment entailment not_entailment entailment not_entailment entailment not_entailment not_entailment entailment not_entailment not_entailment entailment not_entailment entailment entailment not_entailment not_entailment not_entailment entailment entailment not_entailment not_entailment entailment entailment entailment entailment entailment entailment not_entailment not_entailment entailment not_entailment entailment entailment entailment entailment entailment entailment entailment not_entailment not_entailment entailment not_entailment entailment not_entailment entailment entailment entailment entailment entailment not_entailment not_entailment not_entailment entailment not_entailment entailment not_entailment entailment entailment entailment entailment not_entailment not_entailment entailment entailment not_entailment entailment entailment entailment not_entailment not_entailment entailment not_entailment entailment entailment not_entailment not_entailment not_entailment not_entailment entailment not_entailment entailment entailment not_entailment not_entailment not_entailment not_entailment entailment entailment entailment entailment entailment not_entailment entailment entailment not_entailment not_entailment not_entailment not_entailment not_entailment entailment entailment not_entailment entailment not_entailment entailment not_entailment not_entailment not_entailment entailment entailment entailment entailment entailment not_entailment entailment not_entailment not_entailment entailment not_entailment not_entailment entailment not_entailment not_entailment not_entailment not_entailment not_entailment entailment entailment not_entailment entailment entailment entailment entailment entailment not_entailment not_entailment entailment not_entailment not_entailment not_entailment entailment entailment not_entailment not_entailment not_entailment entailment not_entailment entailment entailment not_entailment not_entailment entailment not_entailment not_entailment entailment not_entailment not_entailment entailment entailment entailment not_entailment not_entailment not_entailment entailment not_entailment not_entailment not_entailment entailment not_entailment not_entailment not_entailment entailment not_entailment not_entailment not_entailment not_entailment entailment entailment entailment entailment not_entailment entailment entailment not_entailment not_entailment not_entailment entailment not_entailment not_entailment not_entailment entailment entailment entailment not_entailment not_entailment entailment not_entailment not_entailment not_entailment entailment not_entailment not_entailment not_entailment entailment not_entailment not_entailment entailment not_entailment entailment entailment entailment not_entailment not_entailment entailment entailment not_entailment entailment entailment not_entailment entailment entailment entailment not_entailment not_entailment entailment entailment not_entailment not_entailment entailment not_entailment entailment not_entailment entailment not_entailment not_entailment entailment entailment not_entailment entailment entailment entailment entailment not_entailment not_entailment entailment entailment entailment entailment entailment not_entailment not_entailment entailment not_entailment entailment not_entailment not_entailment not_entailment not_entailment not_entailment entailment entailment entailment entailment entailment not_entailment not_entailment entailment entailment not_entailment entailment entailment entailment not_entailment not_entailment not_entailment entailment not_entailment not_entailment entailment not_entailment not_entailment not_entailment not_entailment not_entailment entailment not_entailment not_entailment not_entailment not_entailment not_entailment entailment entailment not_entailment not_entailment entailment not_entailment entailment entailment not_entailment entailment not_entailment not_entailment entailment not_entailment not_entailment not_entailment entailment not_entailment not_entailment not_entailment not_entailment not_entailment entailment not_entailment not_entailment entailment entailment not_entailment entailment not_entailment not_entailment entailment entailment entailment entailment entailment not_entailment not_entailment not_entailment not_entailment not_entailment not_entailment entailment entailment not_entailment entailment entailment not_entailment entailment not_entailment not_entailment entailment entailment entailment entailment not_entailment entailment entailment entailment entailment entailment entailment not_entailment entailment entailment not_entailment entailment entailment entailment entailment entailment entailment entailment entailment not_entailment entailment entailment entailment entailment not_entailment entailment entailment not_entailment entailment not_entailment not_entailment not_entailment entailment entailment not_entailment entailment entailment not_entailment not_entailment not_entailment not_entailment not_entailment not_entailment entailment entailment entailment entailment entailment not_entailment not_entailment not_entailment entailment entailment not_entailment not_entailment not_entailment entailment not_entailment entailment entailment entailment entailment entailment not_entailment not_entailment entailment not_entailment entailment not_entailment entailment entailment not_entailment not_entailment not_entailment not_entailment not_entailment not_entailment entailment entailment entailment not_entailment not_entailment not_entailment entailment not_entailment entailment not_entailment entailment entailment not_entailment entailment entailment entailment not_entailment not_entailment entailment not_entailment entailment not_entailment not_entailment entailment entailment not_entailment entailment not_entailment entailment not_entailment entailment not_entailment not_entailment entailment entailment not_entailment not_entailment entailment not_entailment not_entailment not_entailment not_entailment not_entailment not_entailment not_entailment entailment entailment entailment not_entailment entailment not_entailment entailment not_entailment entailment not_entailment not_entailment entailment not_entailment entailment not_entailment not_entailment not_entailment not_entailment not_entailment entailment not_entailment entailment not_entailment not_entailment entailment entailment entailment not_entailment not_entailment not_entailment entailment not_entailment entailment entailment not_entailment not_entailment entailment entailment entailment not_entailment not_entailment not_entailment not_entailment entailment entailment not_entailment not_entailment not_entailment not_entailment not_entailment entailment entailment not_entailment entailment not_entailment not_entailment not_entailment entailment not_entailment entailment entailment not_entailment not_entailment not_entailment entailment entailment not_entailment entailment entailment not_entailment entailment not_entailment entailment not_entailment not_entailment not_entailment entailment not_entailment not_entailment not_entailment entailment entailment entailment not_entailment entailment not_entailment not_entailment entailment not_entailment not_entailment entailment not_entailment entailment not_entailment entailment entailment entailment not_entailment entailment not_entailment not_entailment not_entailment entailment not_entailment not_entailment entailment not_entailment not_entailment not_entailment entailment not_entailment entailment not_entailment not_entailment not_entailment not_entailment not_entailment entailment entailment not_entailment entailment not_entailment not_entailment entailment not_entailment not_entailment entailment not_entailment not_entailment not_entailment entailment not_entailment entailment not_entailment entailment not_entailment not_entailment not_entailment not_entailment entailment not_entailment entailment not_entailment not_entailment not_entailment not_entailment entailment not_entailment entailment entailment not_entailment not_entailment not_entailment not_entailment entailment not_entailment entailment entailment entailment not_entailment entailment not_entailment entailment not_entailment entailment not_entailment not_entailment entailment not_entailment entailment entailment not_entailment not_entailment entailment not_entailment not_entailment not_entailment not_entailment entailment entailment entailment entailment not_entailment entailment entailment not_entailment not_entailment not_entailment entailment entailment entailment not_entailment entailment not_entailment entailment not_entailment entailment entailment not_entailment entailment not_entailment entailment entailment entailment not_entailment entailment not_entailment not_entailment entailment not_entailment not_entailment entailment entailment entailment entailment not_entailment entailment entailment entailment not_entailment entailment entailment entailment not_entailment not_entailment entailment not_entailment entailment not_entailment not_entailment not_entailment not_entailment not_entailment entailment not_entailment not_entailment entailment entailment entailment not_entailment not_entailment entailment entailment not_entailment entailment not_entailment entailment not_entailment not_entailment not_entailment entailment not_entailment not_entailment entailment not_entailment not_entailment not_entailment not_entailment entailment entailment entailment not_entailment not_entailment not_entailment not_entailment not_entailment not_entailment entailment entailment not_entailment entailment entailment entailment entailment entailment entailment not_entailment not_entailment not_entailment entailment entailment not_entailment not_entailment entailment entailment entailment entailment not_entailment not_entailment not_entailment not_entailment entailment entailment not_entailment not_entailment entailment entailment not_entailment entailment entailment entailment not_entailment not_entailment not_entailment not_entailment entailment not_entailment not_entailment not_entailment not_entailment not_entailment not_entailment not_entailment not_entailment not_entailment not_entailment not_entailment entailment not_entailment entailment entailment entailment entailment entailment not_entailment not_entailment entailment not_entailment entailment not_entailment entailment entailment not_entailment entailment not_entailment entailment entailment not_entailment not_entailment entailment entailment not_entailment not_entailment entailment not_entailment not_entailment not_entailment not_entailment not_entailment entailment not_entailment entailment not_entailment entailment entailment not_entailment entailment not_entailment not_entailment entailment not_entailment entailment not_entailment entailment entailment not_entailment entailment not_entailment not_entailment entailment entailment entailment entailment entailment entailment not_entailment entailment entailment not_entailment entailment entailment not_entailment not_entailment not_entailment entailment entailment not_entailment entailment entailment entailment not_entailment entailment not_entailment not_entailment not_entailment not_entailment entailment entailment entailment entailment entailment not_entailment entailment entailment entailment not_entailment entailment not_entailment entailment not_entailment entailment entailment not_entailment entailment entailment entailment entailment entailment not_entailment not_entailment entailment not_entailment entailment entailment not_entailment entailment not_entailment entailment not_entailment entailment entailment not_entailment entailment entailment entailment entailment not_entailment not_entailment not_entailment not_entailment entailment not_entailment entailment not_entailment entailment not_entailment entailment entailment entailment entailment entailment entailment entailment not_entailment not_entailment not_entailment not_entailment entailment not_entailment not_entailment entailment entailment entailment not_entailment not_entailment not_entailment not_entailment entailment not_entailment not_entailment entailment entailment entailment not_entailment entailment not_entailment not_entailment not_entailment entailment not_entailment entailment entailment not_entailment entailment not_entailment not_entailment entailment entailment not_entailment not_entailment entailment entailment not_entailment entailment entailment not_entailment entailment entailment entailment entailment entailment entailment not_entailment not_entailment not_entailment entailment not_entailment entailment entailment entailment not_entailment entailment not_entailment entailment not_entailment not_entailment entailment entailment entailment not_entailment not_entailment entailment entailment entailment not_entailment entailment entailment not_entailment entailment entailment entailment entailment not_entailment entailment entailment not_entailment not_entailment not_entailment not_entailment entailment entailment not_entailment entailment not_entailment not_entailment entailment not_entailment not_entailment entailment not_entailment not_entailment not_entailment entailment not_entailment not_entailment entailment entailment entailment entailment not_entailment not_entailment entailment entailment entailment entailment not_entailment not_entailment not_entailment entailment not_entailment entailment not_entailment entailment entailment entailment entailment not_entailment entailment not_entailment entailment entailment entailment not_entailment entailment entailment not_entailment not_entailment entailment not_entailment not_entailment entailment entailment not_entailment not_entailment not_entailment not_entailment not_entailment not_entailment not_entailment not_entailment entailment entailment not_entailment not_entailment entailment entailment entailment not_entailment entailment not_entailment not_entailment not_entailment not_entailment entailment not_entailment entailment entailment not_entailment not_entailment not_entailment entailment entailment not_entailment entailment entailment not_entailment not_entailment not_entailment entailment entailment not_entailment not_entailment not_entailment not_entailment not_entailment not_entailment entailment not_entailment not_entailment entailment not_entailment not_entailment not_entailment entailment not_entailment not_entailment entailment not_entailment entailment entailment entailment entailment not_entailment not_entailment entailment entailment entailment entailment not_entailment not_entailment entailment entailment not_entailment not_entailment not_entailment entailment entailment entailment not_entailment entailment entailment not_entailment not_entailment not_entailment not_entailment not_entailment entailment not_entailment entailment not_entailment not_entailment not_entailment not_entailment entailment entailment not_entailment not_entailment entailment not_entailment not_entailment not_entailment not_entailment entailment entailment not_entailment not_entailment entailment entailment not_entailment entailment not_entailment entailment not_entailment not_entailment not_entailment not_entailment not_entailment entailment not_entailment entailment not_entailment entailment entailment not_entailment not_entailment not_entailment entailment not_entailment entailment not_entailment not_entailment entailment not_entailment not_entailment not_entailment not_entailment not_entailment entailment not_entailment not_entailment not_entailment not_entailment not_entailment entailment entailment not_entailment entailment not_entailment not_entailment not_entailment entailment not_entailment entailment entailment not_entailment not_entailment not_entailment entailment not_entailment entailment not_entailment not_entailment entailment entailment not_entailment not_entailment not_entailment entailment entailment not_entailment entailment entailment not_entailment entailment not_entailment not_entailment entailment entailment not_entailment not_entailment entailment entailment not_entailment not_entailment not_entailment not_entailment not_entailment entailment not_entailment entailment not_entailment not_entailment entailment entailment not_entailment not_entailment entailment entailment not_entailment not_entailment not_entailment not_entailment not_entailment not_entailment not_entailment entailment entailment entailment not_entailment not_entailment entailment entailment not_entailment not_entailment not_entailment entailment not_entailment not_entailment not_entailment not_entailment entailment entailment not_entailment not_entailment entailment not_entailment