def expressionfordateb(corpus, i):
    """
    This function is a helper to check if previous token
    is a digit.

    Args:
        corpus (list), i (int)

    Returns:
        bool
    """
    if i > 0 and corpus[i - 1][0].isdigit() is True and \
     (len(corpus[i - 1]) == 1 or corpus[i - 1][1].isdigit() is True):
        return True
    return False