def MOD(x, y):
    """
    Divides one number by another and returns the remainder.
    See https://docs.mongodb.com/manual/reference/operator/aggregation/mod/
    for more details
    :param x: The number or field is the dividend,
    :param y: The number or field is the divisor,
    :return: Aggregation operator
    """
    return {'$mod': [x, y]}
