-/** a mapping from keys of type <tt>K</tt> to <i>sets</i> of values of type <tt>T</tt> */
-public final class IntPairMap<V> {
+// FEATURE: make this faster (plenty of ways: quadradic probing hash table is one)
+/** a sparse mapping from pairs of <tt>int</tt>'s to <tt>V</tt>'s */
+public final class IntPairMap<V> implements Iterable<V> {