@Override
public int compareTo(Term t) {
if (t == null) return -1;
if (t.isLiteral()) {
Literal tl = (Literal) t;
if (!negated() && tl.negated()) return -1;
else if (negated() && !tl.negated()) return 1;
}
return super.compareTo(t);
}
public LiteralImpl(Literal l) {
super(l);
type = !l.negated();
}