// TREX treats <zeroOrMore> p q </zeroOrMore>
// as <zeroOrMore><group> p q </group></zeroOrMore>
// This method tries to exploit this property to
// simplify the result.
if (exp instanceof SequenceExp) {
SequenceExp seq = (SequenceExp)exp;
visitUnary(seq.exp1);
seq.exp2.visit(this);
} else
exp.visit(this);
}