Negation

class Negation extends CompositeFormula {
    public Negation(Formula formula) {
        super(new Formula[]{formula}, "-");
    }

    public Formula originalFormula() {
        return subf()[0];
    }

    @Override
    public String toString() {
        return "-" + originalFormula().toString();
    }

    @Override
    public Cnf toCnf() {
        Cnf podf = new Cnf();
        podf.addAll(this.originalFormula().toCnf());
        if (podf.size() > 0) {
            podf.remove(0);
        }

        podf.add(new Clause(new Literal(toString()), new Literal(originalFormula().toString())));
        podf.add(new Clause(Literal.Not(originalFormula().toString()), Literal.Not(toString())));

        podf.add(0, new Clause(new Literal(toString())));
        return podf;
    }
}