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Graphical Sequent Calculi for Modal Logics
P. 91-103.
Ma M., Pietarinen A.
The syntax of modal graphs is defined in terms of the continuou
s cut and broken cut following
Charles Peirce’s notation in the gamma part of his graphical
logic of existential graphs. Graphical
calculi for normal modal logics are developed based on a refo
rmulation of the graphical calculus
for classical propositional logic. These graphical calcul
i are of the nature of deep inference. The
relationship between graphical calculi and sequent calcul
i for modal logics is shown by translations
between graphs and modal formulas.