public Exp replace(Exp olde, Exp newe) {
// System.out.println("Exps: "+exps);
if (equals(olde)) return newe;
Exp e;
for (int i = 0; i < exps.size(); i++) {
e = exps.get(i);
if (e.equals(olde)) exps.set(i, newe);
else exps.set(i, e.replace(olde, newe));
e = exps.get(i);
if (e == null) return null;
}
return this;
}
