def remove_keys(doc, keys):
    """Return a new document with keys in keys removed

    >>> doc = {'a':1, 'b':2}
    >>> remove_keys(doc, ['a'])
    {'b': 2}
    >>> # Show that the original document is not affected
    >>> doc['a']
    1
    """
    return dict(
        (k, v) for k, v in doc.items() if k not in keys)