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(*  Title: 	91/Modal/T
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    ID:         $Id$
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    Author: 	Martin Coen
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    Copyright   1991  University of Cambridge
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*)
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T = Modal0 +
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rules
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(* Definition of the star operation using a set of Horn clauses *)
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(* For system T:  gamma * == {P | []P : gamma}                  *)
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(*                delta * == {P | <>P : delta}                  *)
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  lstar0         "|L>"
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  lstar1         "$G |L> $H ==> []P, $G |L> P, $H"
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  lstar2         "$G |L> $H ==>   P, $G |L>    $H"
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  rstar0         "|R>"
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  rstar1         "$G |R> $H ==> <>P, $G |R> P, $H"
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  rstar2         "$G |R> $H ==>   P, $G |R>    $H"
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(* Rules for [] and <> *)
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  boxR
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   "[| $E |L> $E';  $F |R> $F';  $G |R> $G';  \
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\               $E'        |- $F', P, $G'|] ==> $E          |- $F, []P, $G"
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  boxL     "$E, P, $F  |-         $G    ==> $E, []P, $F |-          $G"
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  diaR     "$E         |- $F, P,  $G    ==> $E          |- $F, <>P, $G"
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  diaL
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   "[| $E |L> $E';  $F |L> $F';  $G |R> $G';  \
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\               $E', P, $F'|-         $G'|] ==> $E, <>P, $F |-          $G"
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end
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