Package org.tweetyproject.logics.pl.syntax

Class Equivalence

java.lang.Object

org.tweetyproject.logics.pl.syntax.PlFormula

org.tweetyproject.logics.pl.syntax.Equivalence

All Implemented Interfaces:

Formula, ClassicalFormula, Conjunctable, Disjunctable, Invertable, ProbabilityAware, SimpleLogicalFormula

public class Equivalence
extends PlFormula

This class models equivalence of propositional logic.

Author:

Anna Gessler

Constructor Summary

Constructors

Constructor	Description
Equivalence(Pair<PlFormula,PlFormula> formulas)	Creates a new equivalence with the given pair of formulas
Equivalence(PlFormula a, PlFormula b)	Creates a new equivalence with the given two formulas

Method Summary

Modifier and Type	Method	Description
Equivalence	clone()	Creates a deep copy of this formula
PlFormula	collapseAssociativeFormulas()	This method collapses all associative operations appearing in this term, e.g.
boolean	equals(Object obj)
Set<Proposition>	getAtoms()	Processes the set of all atoms which appear in this formula
Pair<PlFormula,PlFormula>	getFormulas()	Returns the formulas of the equivalence.
Set<PlFormula>	getLiterals()	Returns all literals, i.e.
Set<PossibleWorld>	getModels(PlSignature sig)	Returns the set of models of this formula wrt.
Set<PlPredicate>	getPredicates()	Processes the set of all predicates which appear in this formula
PlSignature	getSignature()	Returns the signature of the language of this formula.
int	hashCode()
int	numberOfOccurrences(Proposition p)	Returns the number of occurrences of the given proposition within this formula
PlFormula	replace(Proposition p, PlFormula f, int i)	Replaces the ith instance of the proposition p by f.
void	setFormulas(Pair<PlFormula,PlFormula> formulas)	Sets the formulas of the equivalence.
void	setFormulas(PlFormula formula1, PlFormula formula2)	Sets the formulas of the equivalence.
Conjunction	toCnf()	This method returns this formula in conjunctive normal form (CNF).
PlFormula	toNnf()	This method returns this formula in negation normal form (NNF).
String	toString()
PlFormula	trim()	Removes duplicates (identical formulas) from conjunctions and disjunctions and removes duplicate negations.

Methods inherited from class org.tweetyproject.logics.pl.syntax.PlFormula

combineWithAnd, combineWithOr, complement, getModels, getPredicateCls, getPrimeImplicants, getUniformProbability, isClause, isConjunctiveClause, isLiteral, resolvableWith, resolveWith, toBlakeCanonicalForm, toDnf

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Constructor Details

Equivalence

public Equivalence(PlFormula a,
 PlFormula b)

Creates a new equivalence with the given two formulas

Parameters:

a - a propositional formula

b - a propositional formula

Equivalence

public Equivalence(Pair<PlFormula,PlFormula> formulas)

Creates a new equivalence with the given pair of formulas

Parameters:

formulas - a pair of formulas

Method Details

getFormulas

public Pair<PlFormula,PlFormula> getFormulas()

Returns the formulas of the equivalence.

Returns:

the formulas that are part of the equivalence

setFormulas

public void setFormulas(Pair<PlFormula,PlFormula> formulas)

Sets the formulas of the equivalence.

Parameters:

formulas - the formulas

setFormulas

public void setFormulas(PlFormula formula1,
 PlFormula formula2)

Sets the formulas of the equivalence.

Parameters:

formula1 - some formula

formula2 - some formula

getAtoms

public Set<Proposition> getAtoms()

Description copied from interface: SimpleLogicalFormula

Processes the set of all atoms which appear in this formula

Specified by:

getAtoms in interface SimpleLogicalFormula

Specified by:

getAtoms in class PlFormula

Returns:

The set of all atoms

getLiterals

public Set<PlFormula> getLiterals()

Description copied from class: PlFormula

Returns all literals, i.e. all formulas of the form "a" or "!a" where "a" is a proposition, that appear in this formula.

Specified by:

getLiterals in class PlFormula

Returns:

all literals appearing in this formula.

collapseAssociativeFormulas

public PlFormula collapseAssociativeFormulas()

Description copied from class: PlFormula

This method collapses all associative operations appearing in this term, e.g. every a||(b||c) becomes a||b||c.

Specified by:

collapseAssociativeFormulas in class PlFormula

Returns:

the collapsed formula.

getPredicates

public Set<PlPredicate> getPredicates()

Description copied from interface: SimpleLogicalFormula

Processes the set of all predicates which appear in this formula

Specified by:

getPredicates in interface SimpleLogicalFormula

Specified by:

getPredicates in class PlFormula

Returns:

all predicates that appear in this formula

trim

public PlFormula trim()

Description copied from class: PlFormula

Removes duplicates (identical formulas) from conjunctions and disjunctions and removes duplicate negations. Simplifies equivalences and implications with equivalent formulas (A=>A, A<=>A) to tautologies.

Specified by:

trim in class PlFormula

Returns:

an equivalent formula without duplicates.

toNnf

public PlFormula toNnf()

Description copied from class: PlFormula

This method returns this formula in negation normal form (NNF). A formula is in NNF iff negations occur only directly in front of a proposition.

Specified by:

toNnf in class PlFormula

Returns:

the formula in NNF.

toCnf

public Conjunction toCnf()

Description copied from class: PlFormula

This method returns this formula in conjunctive normal form (CNF). A formula is in CNF iff it is a conjunction of disjunctions and in NNF. The CNF generated by this method is not necessarily minimal.

Specified by:

toCnf in class PlFormula

Returns:

the formula in CNF.

getModels

public Set<PossibleWorld> getModels(PlSignature sig)

Description copied from class: PlFormula

Returns the set of models of this formula wrt. the given signature.

Specified by:

getModels in class PlFormula

Parameters:

sig - some propositional signature

Returns:

the set of models of this formula wrt. the given signature.

numberOfOccurrences

public int numberOfOccurrences(Proposition p)

Description copied from class: PlFormula

Returns the number of occurrences of the given proposition within this formula

Specified by:

numberOfOccurrences in class PlFormula

Parameters:

p - some proposition

Returns:

the number of occurrences of the given proposition within this formula

replace

public PlFormula replace(Proposition p,
 PlFormula f,
 int i)

Description copied from class: PlFormula

Replaces the ith instance of the proposition p by f.

Specified by:

replace in class PlFormula

Parameters:

p - some proposition

f - some formula

i - the index of the proposition

Returns:

a new formula with the ith instance of the proposition p replaced by f.

hashCode

public int hashCode()

Specified by:

hashCode in interface SimpleLogicalFormula

Specified by:

hashCode in class PlFormula

equals

public boolean equals(Object obj)

Specified by:

equals in interface SimpleLogicalFormula

Specified by:

equals in class PlFormula

clone

public Equivalence clone()

Description copied from interface: SimpleLogicalFormula

Creates a deep copy of this formula

Specified by:

clone in interface SimpleLogicalFormula

Specified by:

clone in class PlFormula

Returns:

the cloned formula

toString

public String toString()

Overrides:

toString in class Object

getSignature

public PlSignature getSignature()

Description copied from interface: Formula

Returns the signature of the language of this formula.

Specified by:

getSignature in interface Formula

Overrides:

getSignature in class PlFormula

Returns:

the signature of the language of this formula.