public Set<Cell<R, C, V>> cellSet() {
      assertTrue(Thread.holdsLock(mutex));
      return delegate.cellSet();
    }

    @Override
    public Map<R, V> column(C columnKey) {
      assertTrue(Thread.holdsLock(mutex));
      return delegate.column(columnKey);
    }

    @Override
    public Set<C> columnKeySet() {
      assertTrue(Thread.holdsLock(mutex));
      return delegate.columnKeySet();
    }

    assertEquals(ImmutableMap.of("foo", 'a', "bar", 'b'), table.column(1));
  }

  // This test assumes that the implementation does not support null keys.
  public void testColumnNull() {
    table = create("foo", 1, 'a', "bar", 1, 'b', "foo", 3, 'c');
    assertThrows(NullPointerException.class, () -> table.column(null));
  }

  public void testColumnSetPartialOverlap() {

    //                                                                    ================
    // -----------------------------------------------------
    //                                       Column Property
    //                                       ---------------
    protected final Map<String, PropertyGateway> _epgMap = newHashMap();
    {
        setupEpg(_epgMap, et -> ((ElevateWordToLabel) et).getElevateWordId(),

    assertEquals(ImmutableSet.of(immutableCell('a', 1, "blah")), testTable.cellSet());
  }

  public void testColumn() {
    assertEquals(ImmutableMap.of(), testTable.column(0));
    assertEquals(ImmutableMap.of('a', "blah"), testTable.column(1));
  }

  public void testColumnKeySet() {
    assertEquals(ImmutableSet.of(1), testTable.columnKeySet());
  }

  public void testColumnMap() {

	args         *ReaderArgs
	readCloser   io.ReadCloser    // raw input
	buf          *bufio.Reader    // input to the splitter
	columnNames  []string         // names of columns
	nameIndexMap map[string]int64 // name to column index
	current      [][]string       // current block of results to be returned
	recordsRead  int              // number of records read in current slice
	input        chan *queueItem  // input for workers

     * @param source The source of the problem, may be {@code null}.
     * @param lineNumber The one-based index of the line containing the error or {@code -1} if unknown.
     * @param columnNumber The one-based index of the column containing the error or {@code -1} if unknown.
     * @param exception The exception that caused this problem, may be {@code null}.
     */
    // mkleint: does this need to be public?
    public DefaultModelProblem(

    //                                                                    ================
    // -----------------------------------------------------
    //                                       Column Property
    //                                       ---------------
    protected final Map<String, PropertyGateway> _epgMap = newHashMap();
    {

    public Set<Cell<R, C, V>> cellSet() {
      assertTrue(Thread.holdsLock(mutex));
      return delegate.cellSet();
    }

    @Override
    public Map<R, V> column(C columnKey) {
      assertTrue(Thread.holdsLock(mutex));
      return delegate.column(columnKey);
    }

    @Override
    public Set<C> columnKeySet() {
      assertTrue(Thread.holdsLock(mutex));
      return delegate.columnKeySet();
    }

    //                                                                    ================
    // -----------------------------------------------------
    //                                       Column Property
    //                                       ---------------
    protected final Map<String, PropertyGateway> _epgMap = newHashMap();
    {
        setupEpg(_epgMap, et -> ((ThumbnailQueue) et).getCreatedBy(),

     * @param lineNumber The one-based index of the line containing the problem or {@code -1} if unknown.
     * @param columnNumber The one-based index of the column containing the problem or {@code -1} if unknown.
     * @param exception The exception that caused this problem, may be {@code null}.
     */
    DefaultProblem(