  Important contributions to the logicality debate that characterize logical constants inferentially in terms of sequent calculus rules are those by Kneale (1956) and Hacking (1979). A thorough account of logicality is proposed by Došen (1980; 1989) in his theory of logical constants as “punctuation marks”, expressing structural features at the logical level. He understands logical constants as being characterized by certain double-line rules for sequents which can be read in both directions. For example, conjunction and disjunction are (in classical logic, with multiple-formulae succedents) characterized by the double-line rules