// checks that the atom has the form f(x) = t[x],
// where f is a function symbol and t[x] is a term of x not containing f
// 09/05/2002, Manchester
bool Atom::isDefinition (Term& lhs, Term& rhs) const
{
TRACER ( "Atom::isDefinition" );
if ( ! isEquality() ) {
return false;
}
// the atom is an equality
Term l (args().head());
Term r (args().second());
if ( l.isvar() || r.isvar() ) {
return false;
}
// l=r, both l and r are non-variables
if ( r.defines(l) ) {
lhs = l;
rhs = r;
return true;
}
if ( l.defines(r) ) {
rhs = l;
lhs = r;
return true;
}
return false;
} // Term* Atom::isDefinition
// return true if the atoms are x = y, P[x] and P[y]
// 29/04/2002 Manchester
bool Atom::predicateMonotonicity (Atom a1, Atom a2, Atom a3)
{
TRACER("Atom::predicateMonotonicity");
if ( ! a1.isEquality() )
return false;
if ( a2.isEquality() )
return false;
if ( a3.isEquality() )
return false;
Term x (a1.args().head());
Term y (a1.args().second());
if ( ! x.isvar() || ! y.isvar() )
return false;
Var vx = x.var();
Var vy = y.var();
// variables must be different
if ( vx == vy )
return false;
if ( a2.functor() != a3.functor() )
return false;
return a2.args().equalUpTo (a3.args(),vx,vy);
} // Atom::predicateMonotonicity