# how to define Skew Polynomial Ring over Cyclotomic Field

how to define Skew Polynomial Ring in x over Cyclotomic Field of order 7 and degree 6 twisted by zeta7 |--> zeta7^2 when i execute those commands

K = CyclotomicField(7)

sigma = K.hom([K.gen()^2])

S.< x > = K['x',sigma]

I have this message error

AssertionError: coercion from Cyclotomic Field of order 7 and degree 6 to Skew Polynomial Ring in x over Cyclotomic Field of order 7 and degree 6 twisted by zeta7 |--> zeta7^2 already registered or discovered