def eresolution(clause) -> list:
res = []
for l in range(len(clause)):
lit = clause.getLiteral(l)
if lit.atom[0] == '=' and lit.isNegative():
left = lit.atom[1]
right = lit.atom[2]
unifier = mgu(left, right)
if unifier is not None:
others = []
for ll in range(len(clause)):
lit2 = clause.getLiteral(ll)
if ll != l:
if unifier is None:
others.append(lit2)
else:
others.append(lit2.instantiate(unifier))
new_clause = Clause(others)
new_clause.setDerivation(
flatDerivation("eresolution", [clause, clause]))
res.append(new_clause)
return res
def termFind(term1, term2):
positions = []
if termIsVar(term1):
return []
subst = mgu(term1, term2)
if isinstance(term1, list):
for i in range(len(term1)):
positions2 = termFind(subterm(term1, [i]), term2)
for p in positions2:
p.add_first(i)
positions.append(p)
if subst is not None:
positions.append(Position(subst))
return positions
def factor(clause, lit1, lit2):
"""
Check if it is possible to form a factor between lit1 and lit2. If
yes, return it, otherwise return None.
"""
l1 = clause.getLiteral(lit1)
l2 = clause.getLiteral(lit2)
if l1.isNegative() != l2.isNegative():
return None
sigma = mgu(l1.atom, l2.atom)
if sigma == None:
return None
lits = [l.instantiate(sigma) for l in clause.literals if l != l2]
res = clauses.Clause(lits)
res.removeDupLits()
res.setDerivation(flatDerivation("factor", [clause]))
return res
def resolution(clause1, lit1, clause2, lit2):
"""
Implementation of the Resolution rule. lit1 and lit2 are indices
of literals in clause1 and clause2, respectively, so clause1|lit1
and clause2|lit2 are literals.
Try to resolve clause1|lit1 against clause2|lit2. If this is
possible, return the resolvent. Otherwise, return None.
"""
l1 = clause1.getLiteral(lit1)
l2 = clause2.getLiteral(lit2)
if l1.isNegative() == l2.isNegative():
return None
sigma = mgu(l1.atom, l2.atom)
if sigma is None:
return None
lits1 = [l.instantiate(sigma) for l in clause1.literals if l!=l1]
lits2 = [l.instantiate(sigma) for l in clause2.literals if l!=l2]
lits1.extend(lits2)
res = clauses.Clause(lits1)
res.removeDupLits()
res.setDerivation(flatDerivation("resolution", [clause1, clause2]))
return res