© The Author, 2005. Published by Oxford University Press. All rights reserved.
Original Articles |
Modal Sequent Calculi Labelled with Truth Values: Cut Elimination
1 CLC, Departamento de Matemática, IST, Av. Rovisco Pais, 1049-001, Lisboa, Portugal. E-mail: pmat{at}math.ist.utl.pt, 2 CLC, Departamento de Matemática, IST, Av. Rovisco Pais, 1049-001, Lisboa, Portugal. E-mail: jfr{at}math.ist.utl.pt, 3 CLC, Departamento de Matemática, IST, Av. Rovisco Pais, 1049-001, Lisboa, Portugal. E-mail: css{at}math.ist.utl.pt
Cut elimination is shown, in a constructive way, to hold in sequent calculi labelled with truth values for a wide class of normal modal logics, supporting global and local reasoning and allowing a general frame semantics. The complexity of cut elimination is studied in terms of the increase of logical depth of the derivations. A hyperexponential worst case bound is established. The subformula property and a similar property for the label terms are shown to be satisfied by that class of modal sequent calculi. Modal logics presented by these calculi are proven to be globally and locally consistent.
Key Words: Cut elimination, complexity of cut elimination, modal sequent calculus, labelled deduction
Received 26 July 2004. Revised 12 January 2005.