I keep getting True for all three test cases. Can you please help me with this question?

Write function arithmetic() that: takes as input a list of numbers and returns True if the numbers in the list form an arithmetic sequence, False otherwise.

Please test your function with following test cases,

>>> arithmetic([3, 6, 9, 12, 15]) True

>>> arithmetic([3, 6, 9, 11, 14]) False

>>> arithmetic([3]) True