# The "in" keyword checks if something exists inside something else
# Always returns a bool — True or False

message = "Hello Bull"

print("Bull" in message)    # True
print("Horn" in message)    # False

# in is case sensitive — exactly like everything else in Python
name = "RedHornDev"

print("Horn" in name)    # True
print("horn" in name)    # False — case sensitive
print("Red" in name)     # True
print("Dev" in name)     # True
print("dev" in name)     # False

# not in — the natural opposite of in
print("Horn" not in message)   # True — Horn is NOT in message
print("Bull" not in message)   # False — Bull IS in message

# Normalize before checking — to avoid case issues
print("horn" in name.lower())  # True — safe approach

# Checking substrings
sentence = "Python is simple and powerful"

print("simple" in sentence)       # True
print("difficult" in sentence)    # False
print("powerful" not in sentence) # False

# With input
username = input("Enter your username: ")
banned = "admin"

print(banned in username)      # True if "admin" appears anywhere
print(banned not in username)  # True if "admin" does NOT appear