def STR_CASE_CMP(x, y):
    """
    Performs case-insensitive comparison of two strings. Returns
        1 if first string is “greater than” the second string.
        0 if the two strings are equal.
        -1 if the first string is “less than” the second string.

    https://docs.mongodb.com/manual/reference/operator/aggregation/strcasecmp/
    for more details
    :param x: The first string or expression of string
    :param y: The second string or expression of string
    :return: Aggregation operator
    """
    return {'$strcasecmp': [x, y]}