return new Negation(r).evaluate();
} else if (r instanceof Division) {
Division d = (Division) r;
if (d.rhs() instanceof ANumber) { // a x/b = a/b x
l = a.divide((ANumber) d.rhs());
r = d.lhs();
}
} else if (r instanceof Multiplication) {
Multiplication m = (Multiplication) r;