if (ret!=null) return ret;
final Relation r = (Relation)pred.relation().accept(this);
switch(pred.name()) {
case ACYCLIC :
ret = (r==pred.relation()) ? pred : r.acyclic();
break;
case FUNCTION :
final RelationPredicate.Function fp = (RelationPredicate.Function) pred;
final Expression domain = fp.domain().accept(this);
final Expression range = fp.range().accept(this);