/**
 * This function takes two sets of customers as input - the overall customers and the subscribed customers.
 * It returns a set of customers who are not subscribed.
 */
fun findUnsubscribedCustomers(customers: Set<String>, subscribedCustomers: Set<String>): Set<String> {

    val unsubscribedCustomers = customers - subscribedCustomers
    return unsubscribedCustomers
}

// Function to send promotional email to unsubscribed customers
/**
 * This function takes two sets of customers as input - the overall customers and the subscribed customers.
 * It returns a set of customers who are not subscribed.
 */
fun findUnsubscribedCustomers(customers: Set<String>, subscribedCustomers: Set<String>): Set<String> {
/**
 * This function takes two sets of customers as input - the overall customers and the subscribed customers.
 * It returns a set of customers who are not subscribed.
 */
fun findUnsubscribedCustomers(customers: Set<String>, subscribedCustomers: Set<String>): Set<String> {

    val unsubscribedCustomers = customers - subscribedCustomers
    return unsubscribedCustomers
}

// Function to send promotional email to unsubscribed customers