////////////////////////////////////////////////////////////////////////////////
+ public Topology noFollow() { return null; }
+
+ Topology toAtom() {
+ if (elements.length>1) throw new RuntimeException("cannot invoke toAtom() on a Sequence with " + elements.length + " elements: " + this);
+ if (elements.length==0) return null;
+ return elements[0].toAtom();
+ }
+
protected final Element[] elements;
final HashSet<Sequence> needs;