# Creating a set
email_addresses = {"user1@example.com", "user2@example.com", "user1@example.com"}
print(f"Initial email addresses (unique): {email_addresses}")

# Adding elements
email_addresses.add("user3@example.com")
email_addresses.add("user2@example.com") # Adding existing element has no effect
print(f"After adding: {email_addresses}")

# Checking for membership (very fast for sets)
print(f"Is user1@example.com present? {'user1@example.com' in email_addresses}")
print(f"Is user4@example.com present? {'user4@example.com' in email_addresses}")

# Removing elements
email_addresses.remove("user3@example.com")
print(f"After removing: {email_addresses}")

# Set operations
subscribers_newsletter_A = {"user1@example.com", "user2@example.com", "user4@example.com"}
subscribers_newsletter_B = {"user2@example.com", "user3@example.com", "user5@example.com"}

# Union: all unique subscribers from A or B
all_subscribers = subscribers_newsletter_A.union(subscribers_newsletter_B)
print(f"All subscribers (A U B): {all_subscribers}")

# Intersection: subscribers common to both A and B
common_subscribers = subscribers_newsletter_A.intersection(subscribers_newsletter_B)
print(f"Common subscribers (A \u2229 B): {common_subscribers}")

# Difference: subscribers in A but not in B
subscribers_A_only = subscribers_newsletter_A.difference(subscribers_newsletter_B)
print(f"Subscribers in A only (A - B): {subscribers_A_only}")

# Symmetric Difference: subscribers in A or B but not both
exclusive_subscribers = subscribers_newsletter_A.symmetric_difference(subscribers_newsletter_B)
print(f"Exclusive subscribers (A \u2296 B): {exclusive_subscribers}")