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formulas.cc
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formulas.cc
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// Copyright (C) 2002--2005 Carnegie Mellon University
// Copyright (C) 2019 Google Inc
//
// This file is part of VHPOP.
//
// VHPOP is free software; you can redistribute it and/or modify it
// under the terms of the GNU General Public License as published by
// the Free Software Foundation; either version 2 of the License, or
// (at your option) any later version.
//
// VHPOP is distributed in the hope that it will be useful, but WITHOUT
// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
// or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
// License for more details.
//
// You should have received a copy of the GNU General Public License
// along with VHPOP; if not, write to the Free Software Foundation,
// Inc., #59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
#include "formulas.h"
#include <iostream>
#include <stack>
#include "bindings.h"
#include "debug.h"
#include "domains.h"
#include "problems.h"
#include "types.h"
/* ====================================================================== */
/* Formula */
/* The true formula. */
const Formula& Formula::TRUE = Constant::TRUE_;
/* The false formula. */
const Formula& Formula::FALSE = Constant::FALSE_;
/* Constructs a formula. */
Formula::Formula()
: ref_count_(0) {
}
/* Deletes this formula. */
Formula::~Formula() {
}
/* Negation operator for formulas. */
const Formula& operator!(const Formula& f) {
const Formula& neg = f.negation();
Formula::register_use(&f);
Formula::unregister_use(&f);
return neg;
}
/* Conjunction operator for formulas. */
const Formula& operator&&(const Formula& f1, const Formula& f2) {
if (f1.contradiction()) {
Formula::register_use(&f2);
Formula::unregister_use(&f2);
return f1;
} else if (f2.contradiction()) {
Formula::register_use(&f1);
Formula::unregister_use(&f1);
return f2;
} else if (f1.tautology()) {
return f2;
} else if (f2.tautology()) {
return f1;
} else if (&f1 == &f2) {
return f1;
} else {
Conjunction& conjunction = *new Conjunction();
const Conjunction* c1 = dynamic_cast<const Conjunction*>(&f1);
if (c1 != NULL) {
for (FormulaList::const_iterator fi = c1->conjuncts().begin();
fi != c1->conjuncts().end(); fi++) {
conjunction.add_conjunct(**fi);
}
Formula::register_use(c1);
Formula::unregister_use(c1);
} else {
conjunction.add_conjunct(f1);
}
const Conjunction* c2 = dynamic_cast<const Conjunction*>(&f2);
if (c2 != NULL) {
for (FormulaList::const_iterator fi = c2->conjuncts().begin();
fi != c2->conjuncts().end(); fi++) {
conjunction.add_conjunct(**fi);
}
Formula::register_use(c2);
Formula::unregister_use(c2);
} else {
conjunction.add_conjunct(f2);
}
return conjunction;
}
}
/* Disjunction operator for formulas. */
const Formula& operator||(const Formula& f1, const Formula& f2) {
if (f1.tautology()) {
Formula::register_use(&f2);
Formula::unregister_use(&f2);
return f1;
} else if (f2.tautology()) {
Formula::register_use(&f1);
Formula::unregister_use(&f1);
return f2;
} else if (f1.contradiction()) {
return f2;
} else if (f2.contradiction()) {
return f1;
} else if (&f1 == &f2) {
return f1;
} else {
Disjunction& disjunction = *new Disjunction();
const Disjunction* d1 = dynamic_cast<const Disjunction*>(&f1);
if (d1 != NULL) {
for (FormulaList::const_iterator fi = d1->disjuncts().begin();
fi != d1->disjuncts().end(); fi++) {
disjunction.add_disjunct(**fi);
}
Formula::register_use(d1);
Formula::unregister_use(d1);
} else {
disjunction.add_disjunct(f1);
}
const Disjunction* d2 = dynamic_cast<const Disjunction*>(&f2);
if (d2 != NULL) {
for (FormulaList::const_iterator fi = d2->disjuncts().begin();
fi != d2->disjuncts().end(); fi++) {
disjunction.add_disjunct(**fi);
}
Formula::register_use(d2);
Formula::unregister_use(d2);
} else {
disjunction.add_disjunct(f2);
}
return disjunction;
}
}
/* ====================================================================== */
/* Constant */
/* Constant representing true. */
const Constant Constant::TRUE_ = Constant(true);
/* Constant representing false. */
const Constant Constant::FALSE_ = Constant(false);
/* Constructs a constant formula. */
Constant::Constant(bool value)
: value_(value) {
register_use(this);
}
/* Returns a formula that separates the given effect from anything
definitely asserted by this formula. */
const Formula& Constant::separator(const Effect& effect,
const Domain& domain) const {
return TRUE;
}
/* Returns this formula subject to the given substitutions. */
const Constant& Constant::substitution(
const std::map<Variable, Term>& subst) const {
return *this;
}
/* Returns an instantiation of this formula. */
const Constant& Constant::instantiation(const std::map<Variable, Term>& subst,
const Problem& problem) const {
return *this;
}
/* Returns the universal base of this formula. */
const Formula& Constant::universal_base(const std::map<Variable, Term>& subst,
const Problem& problem) const {
return *this;
}
/* Prints this formula on the given stream with the given bindings. */
void Constant::print(std::ostream& os,
size_t step_id, const Bindings& bindings) const {
os << (value_ ? "(and)" : "(or)");
}
/* Returns a negation of this formula. */
const Formula& Constant::negation() const {
return value_ ? FALSE : TRUE;
}
/* ====================================================================== */
/* Literal */
/* Next id for ground literals. */
size_t Literal::next_id = 1;
/* Assigns an id to this literal. */
void Literal::assign_id(bool ground) {
if (ground) {
id_ = next_id++;
} else {
id_ = 0;
}
}
/* Returns a formula that separates the given effect from anything
definitely asserted by this formula. */
const Formula& Literal::separator(const Effect& effect,
const Domain& domain) const {
BindingList mgu;
if (Bindings::unifiable(mgu, *this, 1, effect.literal(), 1)) {
Disjunction* disj = NULL;
const Formula* first_d = &FALSE;
for (BindingList::const_iterator bi = mgu.begin(); bi != mgu.end(); bi++) {
const Binding& b = *bi;
if (b.var() != b.term()) {
const Formula& d = Inequality::make(b.var(), b.term());
if (first_d->contradiction()) {
first_d = &d;
} else if (disj == NULL) {
disj = new Disjunction();
disj->add_disjunct(*first_d);
}
if (disj != NULL) {
disj->add_disjunct(d);
}
}
}
if (disj != NULL) {
return *disj;
} else {
return *first_d;
}
}
return TRUE;
}
/* ====================================================================== */
/* Atom */
/* Tests if the two atoms are unifiable, assuming the second atom is
fully instantiated. */
static bool unifiable_atoms(const Atom& a1, const Atom& a2) {
if (a1.predicate() != a2.predicate()) {
return false;
} else {
std::map<Variable, Term> bind;
size_t n = a1.arity();
for (size_t i = 0; i < n; i++) {
Term t1 = a1.term(i);
if (t1.object()) {
if (t1 != a2.term(i)) {
return false;
}
} else {
const Variable& v1 = t1.as_variable();
std::map<Variable, Term>::const_iterator b = bind.find(v1);
if (b != bind.end()) {
if ((*b).second != a2.term(i)) {
return false;
}
} else {
bind.insert(std::make_pair(v1, a2.term(i).as_object()));
}
}
}
return true;
}
}
/* Table of atomic formulas. */
Atom::AtomTable Atom::atoms;
/* Comparison function. */
bool Atom::AtomLess::operator()(const Atom* a1, const Atom* a2) const {
if (a1->predicate() < a2->predicate()) {
return true;
} else if (a2->predicate() < a1->predicate()) {
return false;
} else {
for (size_t i = 0; i < a1->arity(); i++) {
if (a1->term(i) < a2->term(i)) {
return true;
} else if (a2->term(i) < a1->term(i)) {
return false;
}
}
return false;
}
}
/* Returns an atomic state formula with the given predicate and terms. */
const Atom& Atom::make(const Predicate& predicate,
const std::vector<Term>& terms) {
Atom* atom = new Atom(predicate);
bool ground = true;
for (std::vector<Term>::const_iterator ti = terms.begin(); ti != terms.end();
ti++) {
atom->add_term(*ti);
if (ground && (*ti).variable()) {
ground = false;
}
}
if (!ground) {
atom->assign_id(ground);
return *atom;
} else {
std::pair<AtomTable::const_iterator, bool> result = atoms.insert(atom);
if (!result.second) {
delete atom;
return **result.first;
} else {
atom->assign_id(ground);
return *atom;
}
}
}
/* Deletes this atomic formula. */
Atom::~Atom() {
AtomTable::const_iterator ai = atoms.find(this);
if (*ai == this) {
atoms.erase(ai);
}
}
/* Returns this formula subject to the given substitutions. */
const Atom& Atom::substitution(const std::map<Variable, Term>& subst) const {
if (id() > 0) {
return *this;
} else {
std::vector<Term> inst_terms;
bool substituted = false;
for (std::vector<Term>::const_iterator ti = terms_.begin();
ti != terms_.end(); ti++) {
std::map<Variable, Term>::const_iterator si =
(*ti).variable() ? subst.find((*ti).as_variable()) : subst.end();
if (si != subst.end()) {
inst_terms.push_back((*si).second);
substituted = true;
} else {
inst_terms.push_back(*ti);
}
}
if (substituted) {
return make(predicate(), inst_terms);
} else {
return *this;
}
}
}
/* Returns an instantiation of this formula. */
const Formula& Atom::instantiation(const std::map<Variable, Term>& subst,
const Problem& problem) const {
bool substituted = false;
const Atom* inst_atom;
if (id() > 0) {
inst_atom = this;
} else {
std::vector<Term> inst_terms;
for (std::vector<Term>::const_iterator ti = terms_.begin();
ti != terms_.end(); ti++) {
std::map<Variable, Term>::const_iterator si =
(*ti).variable() ? subst.find((*ti).as_variable()) : subst.end();
if (si != subst.end()) {
inst_terms.push_back((*si).second);
substituted = true;
} else {
inst_terms.push_back(*ti);
}
}
inst_atom = substituted ? &make(predicate(), inst_terms) : this;
}
if (PredicateTable::static_predicate(predicate())) {
if (inst_atom->id() > 0) {
if (problem.init_atoms().find(inst_atom) != problem.init_atoms().end()) {
register_use(inst_atom);
unregister_use(inst_atom);
return TRUE;
} else {
register_use(inst_atom);
unregister_use(inst_atom);
return FALSE;
}
} else {
for (AtomSet::const_iterator ai = problem.init_atoms().begin();
ai != problem.init_atoms().end(); ai++) {
if (unifiable_atoms(*inst_atom, **ai)) {
return *inst_atom;
}
}
register_use(inst_atom);
unregister_use(inst_atom);
return FALSE;
}
} else {
return *inst_atom;
}
}
/* Returns the universal base of this formula. */
const Formula& Atom::universal_base(const std::map<Variable, Term>& subst,
const Problem& problem) const {
return instantiation(subst, problem);
}
/* Prints this formula on the given stream with the given bindings. */
void Atom::print(std::ostream& os,
size_t step_id, const Bindings& bindings) const {
os << '(' << predicate();
for (std::vector<Term>::const_iterator ti = terms_.begin();
ti != terms_.end(); ti++) {
os << ' ';
bindings.print_term(os, *ti, step_id);
}
os << ')';
}
/* Returns the negation of this formula. */
const Literal& Atom::negation() const {
return Negation::make(*this);
}
/* ====================================================================== */
/* Negation */
/* Table of negated atoms. */
Negation::NegationTable Negation::negations;
/* Comparison function. */
bool Negation::NegationLess::operator()(const Negation* n1,
const Negation* n2) const {
return &n1->atom() < &n2->atom();
}
/* Returns a negation of the given atom. */
const Negation& Negation::make(const Atom& atom) {
Negation* negation = new Negation(atom);
bool ground = atom.id() > 0;
if (!ground) {
negation->assign_id(ground);
return *negation;
} else {
std::pair<NegationTable::const_iterator, bool> result =
negations.insert(negation);
if (!result.second) {
delete negation;
return **result.first;
} else {
negation->assign_id(ground);
return *negation;
}
}
}
/* Constructs a negated atom. */
Negation::Negation(const Atom& atom)
: atom_(&atom) {
register_use(atom_);
}
/* Deletes this negated atom. */
Negation::~Negation() {
unregister_use(atom_);
NegationTable::const_iterator ni = negations.find(this);
if (*ni == this) {
negations.erase(ni);
}
}
/* Returns this formula subject to the given substitutions. */
const Negation& Negation::substitution(
const std::map<Variable, Term>& subst) const {
if (id() > 0) {
return *this;
} else {
const Atom& f = atom().substitution(subst);
if (&f == atom_) {
return *this;
} else {
return make(f);
}
}
}
/* Returns an instantiation of this formula. */
const Formula& Negation::instantiation(const std::map<Variable, Term>& subst,
const Problem& problem) const {
const Formula& f = atom().instantiation(subst, problem);
if (&f == atom_) {
return *this;
} else {
return !f;
}
}
/* Returns the universal base of this formula. */
const Formula& Negation::universal_base(const std::map<Variable, Term>& subst,
const Problem& problem) const {
return instantiation(subst, problem);
}
/* Prints this formula on the given stream with the given bindings. */
void Negation::print(std::ostream& os,
size_t step_id, const Bindings& bindings) const {
os << "(not ";
atom().print(os, step_id, bindings);
os << ")";
}
/* Returns the negation of this formula. */
const Literal& Negation::negation() const {
return atom();
}
/* ====================================================================== */
/* BindingLiteral */
/* Returns a formula that separates the given effect from anything
definitely asserted by this formula. */
const Formula& BindingLiteral::separator(const Effect& effect,
const Domain& domain) const {
return TRUE;
}
/* ====================================================================== */
/* Equality */
/* Returns an equality of the two terms. */
const Formula& Equality::make(const Term& term1, const Term& term2) {
return make(term1, 0, term2, 0);
}
/* Returns an equality of the two terms. */
const Formula& Equality::make(const Term& term1, size_t id1,
const Term &term2, size_t id2) {
if (term1 == term2 && id1 == id2) {
return TRUE;
} else if (term1.variable()) {
const Type& t1 = TermTable::type(term1);
const Type& t2 = TermTable::type(term2);
if ((term2.variable() && TypeTable::compatible(t1, t2))
|| (term2.object() && TypeTable::subtype(t2, t1))) {
return *new Equality(term1.as_variable(), id1, term2, id2);
} else {
/* The terms have incompatible types. */
return FALSE;
}
} else if (term2.variable()) {
if (TypeTable::subtype(TermTable::type(term1), TermTable::type(term2))) {
return *new Equality(term2.as_variable(), id1, term1, id2);
} else {
/* The terms have incompatible types. */
return FALSE;
}
} else {
/* The two terms are different objects. */
return FALSE;
}
}
/* Returns this formula subject to the given substitutions. */
const Formula& Equality::substitution(
const std::map<Variable, Term>& subst) const {
std::map<Variable, Term>::const_iterator si = subst.find(variable());
const Term& term1 = (si != subst.end()) ? (*si).second : Term(variable());
si = term().variable() ? subst.find(term().as_variable()) : subst.end();
const Term& term2 = (si != subst.end()) ? (*si).second : term();
if (term1 == variable() && term2 == term()) {
return *this;
} else {
return make(term1, step_id1(0), term2, step_id2(0));
}
}
/* Returns an instantiation of this formula. */
const Formula& Equality::instantiation(const std::map<Variable, Term>& subst,
const Problem& problem) const {
return substitution(subst);
}
/* Returns the universal base of this formula. */
const Formula& Equality::universal_base(const std::map<Variable, Term>& subst,
const Problem& problem) const {
return substitution(subst);
}
/* Prints this formula on the given stream with the given bindings. */
void Equality::print(std::ostream& os,
size_t step_id, const Bindings& bindings) const {
os << "(= ";
bindings.print_term(os, variable(), step_id);
os << ' ';
bindings.print_term(os, term(), step_id);
os << ")";
}
/* Returns the negation of this formula. */
const Formula& Equality::negation() const {
return Inequality::make(variable(), step_id1(0), term(), step_id2(0));
}
/* ====================================================================== */
/* Inequality */
/* Returns an equality of the two terms. */
const Formula& Inequality::make(const Term& term1, const Term& term2) {
return make(term1, 0, term2, 0);
}
/* Returns an equality of the two terms. */
const Formula& Inequality::make(const Term& term1, size_t id1,
const Term& term2, size_t id2) {
if (term1 == term2 && id1 == id2) {
return FALSE;
} else if (term1.variable()) {
const Type& t1 = TermTable::type(term1);
const Type& t2 = TermTable::type(term2);
if ((term2.variable() && TypeTable::compatible(t1, t2))
|| (term2.object() && TypeTable::subtype(t2, t1))) {
return *new Inequality(term1.as_variable(), id1, term2, id2);
} else {
/* The terms have incompatible types. */
return TRUE;
}
} else if (term2.variable()) {
if (TypeTable::subtype(TermTable::type(term1), TermTable::type(term2))) {
return *new Inequality(term2.as_variable(), id1, term1, id2);
} else {
/* The terms have incompatible types. */
return TRUE;
}
} else {
/* The two terms are different objects. */
return TRUE;
}
}
/* Returns this formula subject to the given substitutions. */
const Formula& Inequality::substitution(
const std::map<Variable, Term>& subst) const {
std::map<Variable, Term>::const_iterator si = subst.find(variable());
const Term& term1 = (si != subst.end()) ? (*si).second : Term(variable());
si = term().variable() ? subst.find(term().as_variable()) : subst.end();
const Term& term2 = (si != subst.end()) ? (*si).second : term();
if (term1 == variable() && term2 == term()) {
return *this;
} else {
return make(term1, step_id1(0), term2, step_id2(0));
}
}
/* Returns an instantiation of this formula. */
const Formula& Inequality::instantiation(const std::map<Variable, Term>& subst,
const Problem& problem) const {
return substitution(subst);
}
/* Returns the universal base of this formula. */
const Formula& Inequality::universal_base(const std::map<Variable, Term>& subst,
const Problem& problem) const {
return substitution(subst);
}
/* Prints this formula on the given stream with the given bindings. */
void Inequality::print(std::ostream& os,
size_t step_id, const Bindings& bindings) const {
os << "(not (= ";
bindings.print_term(os, variable(), step_id);
os << ' ';
bindings.print_term(os, term(), step_id);
os << "))";
}
/* Returns the negation of this formula. */
const Formula& Inequality::negation() const {
return Equality::make(variable(), step_id1(0), term(), step_id2(0));
}
/* ====================================================================== */
/* Conjunction */
/* Constructs an empty conjunction. */
Conjunction::Conjunction() {}
/* Deletes this conjunction. */
Conjunction::~Conjunction() {
for (FormulaList::const_iterator fi = conjuncts().begin();
fi != conjuncts().end(); fi++) {
unregister_use(*fi);
}
}
/* Adds a conjunct to this conjunction. */
void Conjunction::add_conjunct(const Formula& conjunct) {
conjuncts_.push_back(&conjunct);
register_use(&conjunct);
}
/* Returns a formula that separates the given effect from anything
definitely asserted by this formula. */
const Formula& Conjunction::separator(const Effect& effect,
const Domain& domain) const {
Conjunction* conj = NULL;
const Formula* first_c = &TRUE;
for (FormulaList::const_iterator fi = conjuncts().begin();
fi != conjuncts().end(); fi++) {
const Formula& c = (*fi)->separator(effect, domain);
if (c.contradiction()) {
if (conj == NULL) {
register_use(first_c);
unregister_use(first_c);
} else {
register_use(conj);
unregister_use(conj);
}
return FALSE;
} else if (!c.tautology()) {
if (first_c->tautology()) {
first_c = &c;
} else if (conj == NULL) {
conj = new Conjunction();
conj->add_conjunct(*first_c);
}
if (conj != NULL) {
conj->add_conjunct(c);
}
}
}
if (conj != NULL) {
return *conj;
} else {
return *first_c;
}
}
/* Returns this formula subject to the given substitutions. */
const Formula& Conjunction::substitution(
const std::map<Variable, Term>& subst) const {
Conjunction* conj = NULL;
const Formula* first_c = &TRUE;
bool changed = false;
for (FormulaList::const_iterator fi = conjuncts().begin();
fi != conjuncts().end(); fi++) {
const Formula& c = (*fi)->substitution(subst);
if (&c != *fi) {
changed = true;
}
if (c.contradiction()) {
if (conj == NULL) {
register_use(first_c);
unregister_use(first_c);
} else {
register_use(conj);
unregister_use(conj);
}
return FALSE;
} else if (!c.tautology()) {
if (first_c->tautology()) {
first_c = &c;
} else if (conj == NULL) {
conj = new Conjunction();
conj->add_conjunct(*first_c);
}
if (conj != NULL) {
conj->add_conjunct(c);
}
}
}
if (!changed) {
if (conj == NULL) {
register_use(first_c);
unregister_use(first_c);
} else {
register_use(conj);
unregister_use(conj);
}
return *this;
} else if (conj != NULL) {
return *conj;
} else {
return *first_c;
}
}
/* Returns an instantiation of this formula. */
const Formula& Conjunction::instantiation(const std::map<Variable, Term>& subst,
const Problem& problem) const {
Conjunction* conj = NULL;
const Formula* first_c = &TRUE;
bool changed = false;
for (FormulaList::const_iterator fi = conjuncts().begin();
fi != conjuncts().end(); fi++) {
const Formula& c = (*fi)->instantiation(subst, problem);
if (&c != *fi) {
changed = true;
}
if (c.contradiction()) {
if (conj == NULL) {
register_use(first_c);
unregister_use(first_c);
} else {
register_use(conj);
unregister_use(conj);
}
return FALSE;
} else if (!c.tautology()) {
if (first_c->tautology()) {
first_c = &c;
} else if (conj == NULL) {
conj = new Conjunction();
conj->add_conjunct(*first_c);
}
if (conj != NULL) {
conj->add_conjunct(c);
}
}
}
if (!changed) {
if (conj == NULL) {
register_use(first_c);
unregister_use(first_c);
} else {
register_use(conj);
unregister_use(conj);
}
return *this;
} else if (conj != NULL) {
return *conj;
} else {
return *first_c;
}
}
/* Returns the universal base of this formula. */
const Formula& Conjunction::universal_base(
const std::map<Variable, Term>& subst, const Problem& problem) const {
Conjunction* conj = NULL;
const Formula* first_c = &TRUE;
bool changed = false;
for (FormulaList::const_iterator fi = conjuncts().begin();
fi != conjuncts().end(); fi++) {
const Formula& c = (*fi)->universal_base(subst, problem);
if (&c != *fi) {
changed = true;
}
if (c.contradiction()) {
if (conj == NULL) {
register_use(first_c);
unregister_use(first_c);
} else {
register_use(conj);
unregister_use(conj);
}
return FALSE;
} else if (!c.tautology()) {
if (first_c->tautology()) {
first_c = &c;
} else if (conj == NULL) {
conj = new Conjunction();
conj->add_conjunct(*first_c);
}
if (conj != NULL) {
conj->add_conjunct(c);
}
}
}
if (!changed) {
if (conj == NULL) {
register_use(first_c);
unregister_use(first_c);
} else {
register_use(conj);
unregister_use(conj);
}
return *this;
} else if (conj != NULL) {
return *conj;
} else {
return *first_c;
}
}
/* Prints this formula on the given stream with the given bindings. */
void Conjunction::print(std::ostream& os,
size_t step_id, const Bindings& bindings) const {
os << "(and";
for (FormulaList::const_iterator fi = conjuncts().begin();
fi != conjuncts().end(); fi++) {
os << ' ';
(*fi)->print(os, step_id, bindings);
}
os << ")";
}
/* Returns the negation of this formula. */
const Formula& Conjunction::negation() const {
Disjunction* disj = NULL;
const Formula* first_d = &FALSE;
for (FormulaList::const_iterator fi = conjuncts().begin();
fi != conjuncts().end(); fi++) {
const Formula& d = !**fi;
if (d.tautology()) {
if (disj == NULL) {
register_use(first_d);
unregister_use(first_d);
} else {
register_use(disj);
unregister_use(disj);
}
return TRUE;
} else if (!d.contradiction()) {
if (first_d->contradiction()) {
first_d = &d;
} else if (disj == NULL) {
disj = new Disjunction();
disj->add_disjunct(*first_d);
}
if (disj != NULL) {
disj->add_disjunct(d);
}
}
}
if (disj != NULL) {
return *disj;
} else {
return *first_d;
}
}
/* ====================================================================== */
/* Disjunction */
/* Constructs an empty disjunction. */
Disjunction::Disjunction() {}
/* Deletes this disjunction. */
Disjunction::~Disjunction() {
for (FormulaList::const_iterator fi = disjuncts().begin();
fi != disjuncts().end(); fi++) {
unregister_use(*fi);
}
}
/* Adds a disjunct to this disjunction. */
void Disjunction::add_disjunct(const Formula& disjunct) {
disjuncts_.push_back(&disjunct);
register_use(&disjunct);
}
/* Returns a formula that separates the given effect from anything