On Feb 7, 4:56*pm, amogles wrote:

In a German style Tarifverbund, doubling back is normally allowed, as
the validity of the ticket is zone and time dependent but route
independent.

Indeed. Essentially a "single ticket" in many such cases (not
Hamburg, interestingly, where it is genuinely a single ticket in the
manner of a zonal single Tube ticket) is the same as a day ticket, but
validity is limited to an hour or two.

To prevent silly situations, "you can board any bus within an hour of
first touching in on your first one" or similar is the easiest.

Neil