path: root/src/algebra/logic.spad.pamphlet

\documentclass{article}
\usepackage{open-axiom}

\title{src/algebra logic.spad}
\author{Gabriel Dos~Reis}

\section{category LOGIC Logic}

<<category LOGIC Logic>>=
)abbrev category LOGIC Logic
++ Author: 
++ Date Created:
++ Date Last Changed: May 27, 2009
++ Basic Operations: ~, /\, \/
++ Related Constructors:
++ Keywords: boolean
++ Description:  
++   `Logic' provides the basic operations for lattices,
++   e.g., boolean algebra.
Logic: Category == Type with
    ~:        % -> %
     ++ \spad{~x} returns the logical complement of \spad{x}.
    /\:       (%, %) -> %
     ++ \spad {x/\y} returns the logical `meet', e.g. conjunction, of
     ++ \spad{x} and \spad{y}.
    \/:       (%, %) -> %
     ++ \spad{x\/y} returns the logical `join', e.g. disjunction, or
     ++ \spad{x} and \spad{y}.
  add
    x \/ y == ~(~x /\ ~y)

@

\section{Categories an domains for logic}

<<category BOOLE BooleanLogic>>=
)abbrev category BOOLE BooleanLogic
++ Author: Gabriel Dos Reis
++ Date Created: April 04, 2010
++ Date Last Modified: April 04, 2010
++ Description:
++   This is the category of Boolean logic structures.
BooleanLogic(): Category == Logic with
    not: % -> %
      ++ \spad{not x} returns the complement or negation of \spad{x}.
    and: (%,%) -> %
      ++ \spad{x and y} returns the conjunction of \spad{x} and \spad{y}.
    or: (%,%) -> %
      ++ \spad{x or y} returns the disjunction of \spad{x} and \spad{y}.
  add
    not x == ~ x
    x and y == x /\ y
    x or y == x \/ y
@

<<category PROPLOG PropositionalLogic>>=
)abbrev category PROPLOG PropositionalLogic
++ Author: Gabriel Dos Reis
++ Date Created: Januray 14, 2008
++ Date Last Modified: May 27, 2009
++ Description: This category declares the connectives of
++ Propositional Logic.
PropositionalLogic(): Category == Join(BooleanLogic,SetCategory) with
  true: %
    ++ \spad{true} is a logical constant.
  false: %
    ++ \spad{false} is a logical constant.
  implies: (%,%) -> %
    ++ \spad{implies(p,q)} returns the logical implication of `q' by `p'.
  equiv: (%,%) -> %
    ++ \spad{equiv(p,q)} returns the logical equivalence of `p', `q'.
@

\section{domain PROPFRML PropositionalFormula}
<<domain PROPFRML PropositionalFormula>>=
)set mess autoload on
)abbrev domain PROPFRML PropositionalFormula
++ Author: Gabriel Dos Reis
++ Date Created: Januray 14, 2008
++ Date Last Modified: February, 2011
++ Description: This domain implements propositional formula build
++ over a term domain, that itself belongs to PropositionalLogic
PropositionalFormula(T: SetCategory): Public == Private where
  Public == Join(PropositionalLogic, CoercibleFrom T) with
    isAtom : % -> Maybe T
      ++ \spad{isAtom f} returns a value \spad{v} such that
      ++ \spad{v case T} holds if the formula \spad{f} is a term.

    isNot : % -> Maybe %
      ++ \spad{isNot f} returns a value \spad{v} such that
      ++ \spad{v case %} holds if the formula \spad{f} is a negation.

    isAnd : % -> Maybe Pair(%,%)
      ++ \spad{isAnd f} returns a value \spad{v} such that 
      ++ \spad{v case Pair(%,%)} holds if the formula \spad{f}
      ++ is a conjunction formula.

    isOr : % -> Maybe Pair(%,%)
      ++ \spad{isOr f} returns a value \spad{v} such that 
      ++ \spad{v case Pair(%,%)} holds if the formula \spad{f}
      ++ is a disjunction formula.

    isImplies : % -> Maybe Pair(%,%)
      ++ \spad{isImplies f} returns a value \spad{v} such that 
      ++ \spad{v case Pair(%,%)} holds if the formula \spad{f}
      ++ is an implication formula.

    isEquiv : % -> Maybe Pair(%,%)
      ++ \spad{isEquiv f} returns a value \spad{v} such that 
      ++ \spad{v case Pair(%,%)} holds if the formula \spad{f}
      ++ is an equivalence formula.

    conjunction: (%,%) -> %
      ++ \spad{conjunction(p,q)} returns a formula denoting the
      ++ conjunction of \spad{p} and \spad{q}.

    disjunction: (%,%) -> %
      ++ \spad{disjunction(p,q)} returns a formula denoting the
      ++ disjunction of \spad{p} and \spad{q}.

  Private == add
    Rep == Union(T, Kernel %)
    import Kernel %
    import BasicOperator
    import KernelFunctions2(Identifier,%)
    import List %

    -- Local names for proposition logical operators
    macro FALSE == '%false
    macro TRUE == '%true
    macro NOT == '%not
    macro AND == '%and
    macro OR == '%or
    macro IMP == '%implies
    macro EQV == '%equiv

    -- Return the nesting level of a formula
    level(f: %): NonNegativeInteger ==
      f' := rep f
      f' case T => 0
      height f'

    -- A term is a formula
    coerce(t: T): % == 
      per t

    false == per constantKernel FALSE
    true == per constantKernel TRUE

    ~ p ==
      per kernel(operator(NOT, 1::Arity), [p], 1 + level p)

    conjunction(p,q) ==
      per kernel(operator(AND, 2), [p, q], 1 + max(level p, level q))

    p /\ q == conjunction(p,q)

    disjunction(p,q) ==
      per kernel(operator(OR, 2), [p, q], 1 + max(level p, level q))

    p \/ q == disjunction(p,q)

    implies(p,q) ==
      per kernel(operator(IMP, 2), [p, q], 1 + max(level p, level q))

    equiv(p,q) ==
      per kernel(operator(EQV, 2), [p, q], 1 + max(level p, level q))

    isAtom f ==
      f' := rep f
      f' case T => just(f'@T)
      nothing

    isNot f ==
      f' := rep f
      f' case Kernel(%) and is?(f', NOT) => just(first argument f')
      nothing

    isBinaryOperator(f: Kernel %, op: Symbol): Maybe Pair(%, %) ==
      not is?(f, op) => nothing
      args := argument f
      just pair(first args, second args)

    isAnd f ==
      f' := rep f
      f' case Kernel % => isBinaryOperator(f', AND)
      nothing

    isOr f ==
      f' := rep f
      f' case Kernel % => isBinaryOperator(f', OR)
      nothing

    isImplies f ==
      f' := rep f
      f' case Kernel % => isBinaryOperator(f', IMP)
      nothing


    isEquiv f ==
      f' := rep f
      f' case Kernel % => isBinaryOperator(f', EQV)
      nothing

    -- Unparsing grammar.
    --
    -- Ideally, the following syntax would the external form
    -- Formula:
    --   EquivFormula
    --
    -- EquivFormula:
    --   ImpliesFormula
    --   ImpliesFormula <=> EquivFormula
    --
    -- ImpliesFormula:
    --   OrFormula
    --   OrFormula => ImpliesFormula
    --
    -- OrFormula:
    --   AndFormula
    --   AndFormula or OrFormula 
    -- 
    -- AndFormula
    --   NotFormula
    --   NotFormula and AndFormula
    --
    -- NotFormula:
    --   PrimaryFormula
    --   not NotFormula
    --
    -- PrimaryFormula:
    --   Term
    --   ( Formula )
    --
    -- Note: Since the token '=>' already means a construct different
    --       from what we would like to have as a notation for
    --       propositional logic, we will output the formula `p => q'
    --       as implies(p,q), which looks like a function call.
    --       Similarly, we do not have the token `<=>' for logical
    --       equivalence; so we unparser `p <=> q' as equiv(p,q).
    --
    --       So, we modify the nonterminal PrimaryFormula to read
    --       PrimaryFormula:
    --         Term
    --         implies(Formula, Formula)
    --         equiv(Formula, Formula)
    formula: % -> OutputForm
    coerce(p: %): OutputForm ==
      formula p

    primaryFormula(p: %): OutputForm ==
      p' := rep p
      p' case T => p'@T::OutputForm
      case constantIfCan p' is
        c@Identifier => c::OutputForm
        otherwise =>
          is?(p', IMP) or is?(p', EQV) =>
            args := argument p'
            elt(operator(p')::OutputForm, 
                  [formula first args, formula second args])$OutputForm
          paren(formula p)$OutputForm

    notFormula(p: %): OutputForm ==
      case isNot p is
        f@% => elt(outputForm 'not, [notFormula f])$OutputForm
        otherwise => primaryFormula p

    andFormula(f: %): OutputForm ==
      case isAnd f is
	p@Pair(%,%) =>
          -- ??? idealy, we should be using `and$OutputForm' but
          -- ??? a bug in the compiler currently prevents that.
          infix(outputForm 'and, notFormula first p,
             andFormula second p)$OutputForm
        otherwise => notFormula f

    orFormula(f: %): OutputForm ==
      case isOr f is
        p@Pair(%,%) => 
          -- ??? idealy, we should be using `or$OutputForm' but
          -- ??? a bug in the compiler currently prevents that.
          infix(outputForm 'or, andFormula first p, 
             orFormula second p)$OutputForm
        otherwise => andFormula f

    formula f ==
      -- Note: this should be equivFormula, but see the explanation above.
      orFormula f

@

<<package PROPFUN1 PropositionalFormulaFunctions1>>=
)abbrev package PROPFUN1 PropositionalFormulaFunctions1
++ Author: Gabriel Dos Reis
++ Date Created: April 03, 2010
++ Date Last Modified: April 03, 2010
++ Description:
++   This package collects unary functions operating on propositional
++   formulae.
PropositionalFormulaFunctions1(T): Public == Private where
  T: SetCategory
  Public == Type with
    dual: PropositionalFormula T -> PropositionalFormula T
      ++ \spad{dual f} returns the dual of the proposition \spad{f}.
    atoms: PropositionalFormula T -> Set T
      ++ \spad{atoms f} ++ returns the set of atoms appearing in
      ++ the formula \spad{f}.
    simplify: PropositionalFormula T -> PropositionalFormula T
      ++ \spad{simplify f} returns a formula logically equivalent
      ++ to \spad{f} where obvious tautologies have been removed.
  Private == add
    macro F == PropositionalFormula T
    inline Pair(F,F)

    dual f ==
      f = true$F => false$F
      f = false$F => true$F
      isAtom f case T => f
      (f1 := isNot f) case F => not dual f1
      (f2 := isAnd f) case Pair(F,F) =>
         disjunction(dual first f2, dual second f2)
      (f2 := isOr f) case Pair(F,F) =>
         conjunction(dual first f2, dual second f2)
      error "formula contains `equiv' or `implies'"

    atoms f ==
      (t := isAtom f) case T => { t }
      (f1 := isNot f) case F => atoms f1
      (f2 := isAnd f) case Pair(F,F) =>
         union(atoms first f2, atoms second f2)
      (f2 := isOr f) case Pair(F,F) =>
         union(atoms first f2, atoms second f2)
      empty()$Set(T)

    -- one-step simplification helper function
    simplifyOneStep(f: F): F ==
      (f1 := isNot f) case F =>
        f1 = true$F => false$F
        f1 = false$F => true$F
        (f1' := isNot f1) case F => f1'         -- assume classical logic
        f
      (f2 := isAnd f) case Pair(F,F) =>
        first f2 = false$F or second f2 = false$F => false$F
        first f2 = true$F => second f2
        second f2 = true$F => first f2
        f
      (f2 := isOr f) case Pair(F,F) =>
        first f2 = false$F => second f2
        second f2 = false$F => first f2
        first f2 = true$F or second f2 = true$F => true$F
        f
      (f2 := isImplies f) case Pair(F,F) =>
        first f2 = false$F or second f2 = true$F => true$F
        first f2 = true$F => second f2
        second f2 = false$F => not first f2
        f
      (f2 := isEquiv f) case Pair(F,F) =>
        first f2 = true$F => second f2
        second f2 = true$F => first f2
        first f2 = false$F => not second f2
        second f2 = false$F => not first f2
        f
      f

    simplify f ==
      (f1 := isNot f) case F => simplifyOneStep(not simplify f1)
      (f2 := isAnd f) case Pair(F,F) =>
        simplifyOneStep(conjunction(simplify first f2, simplify second f2))
      (f2 := isOr f) case Pair(F,F) =>
        simplifyOneStep(disjunction(simplify first f2, simplify second f2))
      (f2 := isImplies f) case Pair(F,F) =>
        simplifyOneStep(implies(simplify first f2, simplify second f2))
      (f2 := isEquiv f) case Pair(F,F) =>
        simplifyOneStep(equiv(simplify first f2, simplify second f2))
      f
@

<<package PROPFUN2 PropositionalFormulaFunctions2>>=
)abbrev package PROPFUN2 PropositionalFormulaFunctions2
++ Author: Gabriel Dos Reis
++ Date Created: April 03, 2010
++ Date Last Modified: April 03, 2010
++ Description:
++   This package collects binary functions operating on propositional
++   formulae.
PropositionalFormulaFunctions2(S,T): Public == Private where
  S: SetCategory
  T: SetCategory
  Public == Type with
    map: (S -> T, PropositionalFormula S) -> PropositionalFormula T
      ++ \spad{map(f,x)} returns a propositional formula where
      ++ all atoms in \spad{x} have been replaced by the result
      ++ of applying the function \spad{f} to them.
  Private == add
    macro FS == PropositionalFormula S
    macro FT == PropositionalFormula T
    map(f,x) ==
      x = true$FS => true$FT
      x = false$FS => false$FT
      (t := isAtom x) case S => f(t)::FT
      (f1 := isNot x) case FS => not map(f,f1)
      (f2 := isAnd x) case Pair(FS,FS) =>
         conjunction(map(f,first f2), map(f,second f2))
      (f2 := isOr x) case Pair(FS,FS) =>
         disjunction(map(f,first f2), map(f,second f2))
      (f2 := isImplies x) case Pair(FS,FS) =>
         implies(map(f,first f2), map(f,second f2))
      (f2 := isEquiv x) case Pair(FS,FS) =>
         equiv(map(f,first f2), map(f,second f2))
      error "invalid propositional formula"

@


\section{Kleene's Three-Valued Logic}
<<domain KTVLOGIC KleeneTrivalentLogic>>=
)abbrev domain KTVLOGIC KleeneTrivalentLogic
++ Author: Gabriel Dos Reis
++ Date Created: September 20, 2008
++ Date Last Modified: January 14, 2012
++ Description: 
++   This domain implements Kleene's 3-valued propositional logic.
KleeneTrivalentLogic(): Public == Private where
  Public == Join(PropositionalLogic,Finite) with
    unknown: %     ++ the indefinite `unknown' 
    case: (%,[| false |]) -> Boolean
      ++ x case false holds if the value of `x' is `false'
    case: (%,[| unknown |]) -> Boolean
      ++ x case unknown holds if the value of `x' is `unknown'
    case: (%,[| true |]) -> Boolean
      ++ s case true holds if the value of `x' is `true'.
  Private == Maybe Boolean add
    false == per just(false@Boolean)
    unknown == per nothing
    true == per just(true@Boolean)
    x = y == rep x = rep y
    x case true == x = true@%
    x case false == x = false@%
    x case unknown == x = unknown

    not x ==
      x case false => true
      x case unknown => unknown
      false

    x and y ==
      x case false => false
      x case unknown =>
        y case false => false
        unknown
      y

    x or y ==
      x case false => y
      x case true => x
      y case true => y
      unknown

    implies(x,y) ==
      x case false => true
      x case true => y
      y case true => true
      unknown

    equiv(x,y) ==
      x case unknown => x
      x case true => y
      not y

    coerce(x: %): OutputForm ==
      case rep x is
        y@Boolean => y::OutputForm
        otherwise => outputForm 'unknown

    size() == 3

    index n ==
      n > 3 => error "index: argument out of bound"
      n = 1 => false
      n = 2 => unknown
      true

    lookup x ==
      x = false => 1
      x = unknown => 2
      3
@

\section{License}

<<license>>=
--Copyright (C) 1991-2002, The Numerical Algorithms Group Ltd.
--All rights reserved.
--Copyright (C) 2007-2013, Gabriel Dos Reis.
--All rights reserved.
--
--Redistribution and use in source and binary forms, with or without
--modification, are permitted provided that the following conditions are
--met:
--
--    - Redistributions of source code must retain the above copyright
--      notice, this list of conditions and the following disclaimer.
--
--    - Redistributions in binary form must reproduce the above copyright
--      notice, this list of conditions and the following disclaimer in
--      the documentation and/or other materials provided with the
--      distribution.
--
--    - Neither the name of The Numerical Algorithms Group Ltd. nor the
--      names of its contributors may be used to endorse or promote products
--      derived from this software without specific prior written permission.
--
--THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
--IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
--TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
--PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER
--OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
--EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
--PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
--PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
--LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
--NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
--SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
@
<<*>>=
<<license>>

<<category LOGIC Logic>>
<<category BOOLE BooleanLogic>>

<<category PROPLOG PropositionalLogic>>
<<domain PROPFRML PropositionalFormula>>
<<package PROPFUN1 PropositionalFormulaFunctions1>>
<<package PROPFUN2 PropositionalFormulaFunctions2>>

<<domain KTVLOGIC KleeneTrivalentLogic>>

@


\eject
\begin{thebibliography}{99}
\bibitem{1} nothing
\end{thebibliography}
\end{document}