@Test public void furan_augment() throws Exception {

    Graph g = Graph.fromSmiles("o1cccc1");
    IntSet s = IntSet.allOf(1, 2, 3, 4); // exclude the oxygen
    Matching m = Matching.empty(g);
    m.match(2, 3);
    MaximumMatching.maximise(g, m, 2, s);
    assertThat(m.matches(), hasItems(Tuple.of(1, 2),
                                     Tuple.of(3, 4)));
}