+ public Union add(Sequence s) {
+ if (viewed)
+ throw new RuntimeException("once Union.contains() or Union.iterator() has been invoked, "+
+ "you may not add any more Sequences to it\n "+
+ " union in question: " + this);
+ if (s.needed_or_hated)
+ throw new RuntimeException("you may not add a conjunct directly to a Union");
+ s.in_a_union = true;
+ if (alternatives.contains(s)) return this;