this is one example, but in the S2 they have mentioned that it must have overlapped candidate keys. which i felt it need not be true because we can have so many example proving the S2 AS wrong.
eg: R(ABCD)
AB->CD, C->B
in the given relation we don't need any overlapped keys but it is in 3NF but NOT IN BCNF.
correct me , if my approach towards the question is wrong.