Operator '-' is not supported by list data structure, hence you are getting that error. You can compute the difference using one of the following approaches.
Approach 1: if you are concerned about the sequence of the elements and do not care about the runtime.
>>> f
[9, 11, 1, 13, 4, 5, 3, 12, 14, 10, 2, 7, 8, 6]
>>> c
[1, 2, 3]
>>> diff=[i for i in f if i not in c]
>>> diff
[9, 11, 13, 4, 5, 12, 14, 10, 7, 8, 6]
Other approaches are based on set operations, so the order of elements will not be preserved.
>>> list(set(f).difference(c))
[4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14]
>>> list(set(f)-set(c))
[4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14]
>>> list(set(f)^set(c))
[4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14]