contacts = {
  "tom": "122-444-333",
  "jim": "412-1231-121",
  "ron": "8912-121-1212",
  "jake": "333-1881-121"
}


print("jane" in contacts)     # Does key 'jane' exists in contacts?

print("ron" in contacts)      # Does key 'ron' exists in contacts?

print("tom" not in contacts)   # Doesn't key 'tom' exists in contacts