On "jumping the shark":
IMO, it has just become to mean the point at which a program goes downhill, regardless of
how and why Happy Days performed the act.
On Happy Days:
Yes they did show lay seventies. Some of their background music was distinctly 1970s
funk based you also heard on contemporary set series.
On British TV comedies:
I used to watch one called Allo Allo (I think that was it's name), it was about the goings on at a Sally-Anne place. Seen all the Beans. Las I seen MPFC on US TV was on A&E (cable channel). It was also on the Canadian comedy channel.
