List of all arXiv categories that ever existed.

    Example:
        >>> from inspire_schemas.utils import valid_arxiv_categories
        >>> 'funct-an' in valid_arxiv_categories()
        True

def valid_arxiv_categories():
    """List of all arXiv categories that ever existed.

    Example:
        >>> from inspire_schemas.utils import valid_arxiv_categories
        >>> 'funct-an' in valid_arxiv_categories()
        True

    """
    schema = load_schema('elements/arxiv_categories')
    categories = schema['enum']
    categories.extend(_NEW_CATEGORIES.keys())

    return categories