code: private void coverColumn(ColumnHeader<ColumnName> col) {
      LOG.debug("cover " + col.head.name);
      // remove the column
      col.right.left = col.left;
      col.left.right = col.right;
      Node<ColumnName> row = col.down;
      while (row != col) {
        Node<ColumnName> node = row.right;
        while (node != row) {
          node.down.up = node.up;
          node.up.down = node.down;
          node.head.size -= 1;
          node = node.right;
        }
        row = row.down;
      }
    }
docs: Hide a column in the table
  @param col the column to hide