Read corpus from file and return a frozenset

    :param string filename: file corpus

def get_corpus(filename: str) -> frozenset:
    """
    Read corpus from file and return a frozenset

    :param string filename: file corpus
    """
    lines = []
    with open(os.path.join(corpus_path(), filename), "r", encoding="utf-8-sig") as fh:
        lines = fh.read().splitlines()

    return frozenset(lines)