TY - JOUR Y1 - 1999/// JF - RAIRO - Theoretical Informatics and Applications AV - none SP - 447 KW - Semantics; regular expressions; axiomatizations; bisimulation. ID - eprints344 IS - 4/5 UR - http://dx.doi.org/10.1051/ita:1999127 PB - Cambridge University Press VL - 33 A1 - Corradini, Flavio A1 - De Nicola, Rocco A1 - Labella, Anna N1 - Mathematics Subject Classification: 68Q55; 68Q68; 08B05 N2 - An alternative (tree-based) semantics for a class of regular expressions is proposed that assigns a central rôle to the + operator and thus to nondeterminism and nondeterministic choice. For the new semantics a consistent and complete axiomatization is obtained from the original axiomatization of regular expressions by Salomaa and by Kozen by dropping the idempotence law for + and the distribution law of ? over +. EP - 466 TI - A finite axiomatization of nondeterministic regular expressions ER -