Bob Adams wrote:
Because there are no Oyster readers.


The WAGN grippers carry them and I have seen with my own eyes that
they
accept them as valid to stations as far as New Barnet.


That would be a season ticket on Oyster which is valid everywhere a
paper season ticket is. Prepay is a different matter because it
requires pads which read and write at the begining and end of the
journey (in order to charge and record the journey).

--
Chris