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(* Title: Sequents/S4.thy
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Author: Martin Coen
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Copyright 1991 University of Cambridge
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*)
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theory S4
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imports Modal0
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begin
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axiomatization where
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(* Definition of the star operation using a set of Horn clauses *)
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(* For system S4: gamma * == {[]P | []P : gamma} *)
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(* delta * == {<>P | <>P : delta} *)
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lstar0: "|L>" and
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lstar1: "$G |L> $H ==> []P, $G |L> []P, $H" and
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lstar2: "$G |L> $H ==> P, $G |L> $H" and
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rstar0: "|R>" and
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rstar1: "$G |R> $H ==> <>P, $G |R> <>P, $H" and
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rstar2: "$G |R> $H ==> P, $G |R> $H" and
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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, $G" and
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boxL: "$E,P,$F,[]P |- $G ==> $E, []P, $F |- $G" and
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diaR: "$E |- $F,P,$G,<>P ==> $E |- $F, <>P, $G" and
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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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ML {*
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structure S4_Prover = Modal_ProverFun
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(
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val rewrite_rls = @{thms rewrite_rls}
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val safe_rls = @{thms safe_rls}
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val unsafe_rls = @{thms unsafe_rls} @ [@{thm boxR}, @{thm diaL}]
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val bound_rls = @{thms bound_rls} @ [@{thm boxL}, @{thm diaR}]
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val aside_rls = [@{thm lstar0}, @{thm lstar1}, @{thm lstar2}, @{thm rstar0},
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@{thm rstar1}, @{thm rstar2}]
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)
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*}
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method_setup S4_solve = {* Scan.succeed (K (SIMPLE_METHOD (S4_Prover.solve_tac 2))) *}
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(* Theorems of system T from Hughes and Cresswell and Hailpern, LNCS 129 *)
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lemma "|- []P --> P" by S4_solve
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lemma "|- [](P-->Q) --> ([]P-->[]Q)" by S4_solve (* normality*)
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lemma "|- (P--<Q) --> []P --> []Q" by S4_solve
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lemma "|- P --> <>P" by S4_solve
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lemma "|- [](P & Q) <-> []P & []Q" by S4_solve
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lemma "|- <>(P | Q) <-> <>P | <>Q" by S4_solve
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lemma "|- [](P<->Q) <-> (P>-<Q)" by S4_solve
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lemma "|- <>(P-->Q) <-> ([]P--><>Q)" by S4_solve
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lemma "|- []P <-> ~<>(~P)" by S4_solve
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lemma "|- [](~P) <-> ~<>P" by S4_solve
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lemma "|- ~[]P <-> <>(~P)" by S4_solve
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lemma "|- [][]P <-> ~<><>(~P)" by S4_solve
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lemma "|- ~<>(P | Q) <-> ~<>P & ~<>Q" by S4_solve
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lemma "|- []P | []Q --> [](P | Q)" by S4_solve
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lemma "|- <>(P & Q) --> <>P & <>Q" by S4_solve
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lemma "|- [](P | Q) --> []P | <>Q" by S4_solve
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lemma "|- <>P & []Q --> <>(P & Q)" by S4_solve
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lemma "|- [](P | Q) --> <>P | []Q" by S4_solve
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lemma "|- <>(P-->(Q & R)) --> ([]P --> <>Q) & ([]P--><>R)" by S4_solve
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lemma "|- (P--<Q) & (Q--<R) --> (P--<R)" by S4_solve
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lemma "|- []P --> <>Q --> <>(P & Q)" by S4_solve
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(* Theorems of system S4 from Hughes and Cresswell, p.46 *)
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lemma "|- []A --> A" by S4_solve (* refexivity *)
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lemma "|- []A --> [][]A" by S4_solve (* transitivity *)
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lemma "|- []A --> <>A" by S4_solve (* seriality *)
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lemma "|- <>[](<>A --> []<>A)" by S4_solve
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lemma "|- <>[](<>[]A --> []A)" by S4_solve
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lemma "|- []P <-> [][]P" by S4_solve
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lemma "|- <>P <-> <><>P" by S4_solve
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lemma "|- <>[]<>P --> <>P" by S4_solve
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lemma "|- []<>P <-> []<>[]<>P" by S4_solve
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lemma "|- <>[]P <-> <>[]<>[]P" by S4_solve
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(* Theorems for system S4 from Hughes and Cresswell, p.60 *)
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lemma "|- []P | []Q <-> []([]P | []Q)" by S4_solve
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lemma "|- ((P>-<Q) --< R) --> ((P>-<Q) --< []R)" by S4_solve
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(* These are from Hailpern, LNCS 129 *)
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lemma "|- [](P & Q) <-> []P & []Q" by S4_solve
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lemma "|- <>(P | Q) <-> <>P | <>Q" by S4_solve
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lemma "|- <>(P --> Q) <-> ([]P --> <>Q)" by S4_solve
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lemma "|- [](P --> Q) --> (<>P --> <>Q)" by S4_solve
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lemma "|- []P --> []<>P" by S4_solve
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lemma "|- <>[]P --> <>P" by S4_solve
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lemma "|- []P | []Q --> [](P | Q)" by S4_solve
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lemma "|- <>(P & Q) --> <>P & <>Q" by S4_solve
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lemma "|- [](P | Q) --> []P | <>Q" by S4_solve
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lemma "|- <>P & []Q --> <>(P & Q)" by S4_solve
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lemma "|- [](P | Q) --> <>P | []Q" by S4_solve
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end
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