@Override
	protected void addTransition(ItemPair from, Transition t1, Transition t2, ItemPair to) {
		if (to != null) {
			final PairTransition pt = new PairTransition(from, t1, t2, to);
			transitions.add(pt);
			if (to.equalItems() && !from.equalItems() && 
					((t1 != null && t1.getType() == Reduce.class) || 
					 (t2 != null && t2.getType() == Reduce.class))) {
				potentialAmbiguities.add(pt);
			}
			super.addTransition(from, t1, t2, to);
		}
	}