Bug in polynomial ring over quotient ring of multivariate polynomial ring?

[Peter Mueller]

Is it a bug, or is there a reasonable explanation of the following?

kk.<a,b> = GF(2)[]

k.<y,w> = kk.quo(a^2+a+1)

K.<T> = k[]

for n in [10..32]:

    print n, (T*y)^n

0 y*T^10

11 (y + 1)*T^11

12 T^12

13 y*T^13

14 (y + 1)*T^14

15 T^15

16 y*T^16

17 (y + 1)*T^17

18 T^18

19 y*T^19

20 (y + 1)*T^20

21---------------------------------------------------------------------------

NotImplementedError                       Traceback (most recent call last)

[...]

--> 986         return self.base_ring().characteristic()

    987 

    988     def cyclotomic_polynomial(self, n):

[...]

/home/mueller/local/sage-8.0/local/lib/python2.7/site-packages/sage/rings/quotient_ring.pyc in characteristic(self)

    757             NotImplementedError

    758         """

--> 759         raise NotImplementedError

    760 

    761     def defining_ideal(self):

NotImplementedError: 

sage: 

-- Peter Mueller

[Vincent Delecroix]

Not really a bug but it is indeed annoying. I provided a fix for this
very specific problem

https://trac.sagemath.org/ticket/24308

And opened an issue for the more general problem of the fact that
quotient rings do not know their characteristic

https://trac.sagemath.org/ticket/24309

Vincent