%------------------------------------------------------------------------------
% File     : LCL008^0 : TPTP v9.0.0. Released v3.6.0.
% Domain   : Logical Calculi (Modal Logic)
% Axioms   : Multi-Modal Logic
% Version  : [Ben08] axioms : Especial.
% English  :

% Refs     : [Ben08] Benzmueller (2008), Email to G. Sutcliffe
%          : [BP08]  Benzmueller & Paulson (2009), Exploring Properties of
% Source   : [Ben08]
% Names    : MODAL_LOGIC [Ben08]

% Status   : Satisfiable
% Syntax   : Number of formulae    :   35 (  15 unt;  20 typ;  15 def)
%            Number of atoms       :   37 (  15 equ;   0 cnn)
%            Maximal formula atoms :    1 (   1 avg)
%            Number of connectives :   35 (   3   ~;   1   |;   2   &;  28   @)
%                                         (   0 <=>;   1  =>;   0  <=;   0 <~>)
%            Maximal formula depth :    1 (   1 avg;  28 nst)
%            Number of types       :    3 (   1 usr)
%            Number of type conns  :   79 (  79   >;   0   *;   0   +;   0  <<)
%            Number of symbols     :   22 (  19 usr;   3 con; 0-3 aty)
%            Number of variables   :   36 (  28   ^   4   !;   4   ?;  36   :)
% SPC      : 

% Comments : THF0 syntax
%------------------------------------------------------------------------------
%----Our possible worlds are are encoded as terms the type  $i;
%----Here is a constant for the current world:
thf(current_world,type,
    current_world: $i ).

%----Modal logic propositions are then becoming predicates of type ( $i> $o);
%----We introduce some atomic multi-modal logic propositions as constants of
%----type ( $i> $o):
thf(prop_a,type,
    prop_a: $i > $o ).

thf(prop_b,type,
    prop_b: $i > $o ).

thf(prop_c,type,
    prop_c: $i > $o ).

%----The idea is that an atomic multi-modal logic proposition P (of type
%---- $i >  $o) holds at a world W (of type  $i) iff W is in P resp. (P @ W)
%----Now we define the multi-modal logic connectives by reducing them to set
%----operations
%----mfalse corresponds to emptyset (of type $i)
thf(mfalse_decl,type,
    mfalse: $i > $o ).

thf(mfalse,definition,
    ( mfalse
    = ( ^ [X: $i] : $false ) ) ).

%----mtrue corresponds to the universal set (of type $i)
thf(mtrue_decl,type,
    mtrue: $i > $o ).

thf(mtrue,definition,
    ( mtrue
    = ( ^ [X: $i] : $true ) ) ).

%----mnot corresponds to set complement
thf(mnot_decl,type,
    mnot: ( $i > $o ) > $i > $o ).

thf(mnot,definition,
    ( mnot
    = ( ^ [X: $i > $o,U: $i] :
          ~ ( X @ U ) ) ) ).

%----mor corresponds to set union
thf(mor_decl,type,
    mor: ( $i > $o ) > ( $i > $o ) > $i > $o ).

thf(mor,definition,
    ( mor
    = ( ^ [X: $i > $o,Y: $i > $o,U: $i] :
          ( ( X @ U )
          | ( Y @ U ) ) ) ) ).

%----mand corresponds to set intersection
thf(mand_decl,type,
    mand: ( $i > $o ) > ( $i > $o ) > $i > $o ).

thf(mand,definition,
    ( mand
    = ( ^ [X: $i > $o,Y: $i > $o,U: $i] :
          ( ( X @ U )
          & ( Y @ U ) ) ) ) ).

%----mimpl defined via mnot and mor
thf(mimpl_decl,type,
    mimpl: ( $i > $o ) > ( $i > $o ) > $i > $o ).

thf(mimpl,definition,
    ( mimpl
    = ( ^ [U: $i > $o,V: $i > $o] : ( mor @ ( mnot @ U ) @ V ) ) ) ).

%----miff defined via mand and mimpl
thf(miff_decl,type,
    miff: ( $i > $o ) > ( $i > $o ) > $i > $o ).

thf(miff,definition,
    ( miff
    = ( ^ [U: $i > $o,V: $i > $o] : ( mand @ ( mimpl @ U @ V ) @ ( mimpl @ V @ U ) ) ) ) ).

%----mbox
thf(mbox_decl,type,
    mbox: ( $i > $i > $o ) > ( $i > $o ) > $i > $o ).

thf(mbox,definition,
    ( mbox
    = ( ^ [R: $i > $i > $o,P: $i > $o,X: $i] :
        ! [Y: $i] :
          ( ( R @ X @ Y )
         => ( P @ Y ) ) ) ) ).

%----mdia
thf(mdia_decl,type,
    mdia: ( $i > $i > $o ) > ( $i > $o ) > $i > $o ).

thf(mdia,definition,
    ( mdia
    = ( ^ [R: $i > $i > $o,P: $i > $o,X: $i] :
        ? [Y: $i] :
          ( ( R @ X @ Y )
          & ( P @ Y ) ) ) ) ).

%----For mall and mexists, i.e., first order modal logic, we declare a new
%----base type individuals
thf(individuals_decl,type,
    individuals: $tType ).

%----mall
thf(mall_decl,type,
    mall: ( individuals > $i > $o ) > $i > $o ).

thf(mall,definition,
    ( mall
    = ( ^ [P: individuals > $i > $o,W: $i] :
        ! [X: individuals] : ( P @ X @ W ) ) ) ).

%----mexists
thf(mexists_decl,type,
    mexists: ( individuals > $i > $o ) > $i > $o ).

thf(mexists,definition,
    ( mexists
    = ( ^ [P: individuals > $i > $o,W: $i] :
        ? [X: individuals] : ( P @ X @ W ) ) ) ).

%----Validity of a multi modal logic formula can now be encoded as
thf(mvalid_decl,type,
    mvalid: ( $i > $o ) > $o ).

thf(mvalid,definition,
    ( mvalid
    = ( ^ [P: $i > $o] :
        ! [W: $i] : ( P @ W ) ) ) ).

%----Satisfiability of a multi modal logic formula can now be encoded as
thf(msatisfiable_decl,type,
    msatisfiable: ( $i > $o ) > $o ).

thf(msatisfiable,definition,
    ( msatisfiable
    = ( ^ [P: $i > $o] :
        ? [W: $i] : ( P @ W ) ) ) ).

%----Countersatisfiability of a multi modal logic formula can now be encoded as
thf(mcountersatisfiable_decl,type,
    mcountersatisfiable: ( $i > $o ) > $o ).

thf(mcountersatisfiable,definition,
    ( mcountersatisfiable
    = ( ^ [P: $i > $o] :
        ? [W: $i] :
          ~ ( P @ W ) ) ) ).

%----Invalidity of a multi modal logic formula can now be encoded as
thf(minvalid_decl,type,
    minvalid: ( $i > $o ) > $o ).

thf(minvalid,definition,
    ( minvalid
    = ( ^ [P: $i > $o] :
        ! [W: $i] :
          ~ ( P @ W ) ) ) ).

%------------------------------------------------------------------------------