[r-t] Proposed definition of a peal

[Mark Davies]

How about a peal is true if:

1. It is rung on one stage, and each change in the extent at this stage is
rung either N or N+1 times in the peal, and no more, for N>=0.

2. It is rung on two stages, A and B, where |B-A|=1, and each change in the
extent on A is rung M times in the peal, and no more, and each change in the
extent on B is rung N or N+1 times, and no more, for M>0 and N>0.

3. Peals of methods at different stages may be rung as a single-stage peal
as (1) above by considering the covering bell two be included in the change
for methods at the lower stage.

What this basically says is, if you're ringing a peal where whole extents
are involved, then the "weaker" truth pattern serves: you just have to make
sure the extents or part extents for each stage are true against themselves.
This is hopefully covered by point 2: the point of the "N>0" here is to make
sure at least one whole extent is rung of each stage, making the weak a bit
stronger again.

I've added an extra consideration to prevent part-extents being rung at both
stages. So you could have an extent of Minor and an extent of Triples and a
short touch of Triples, or an extent of Triples and an extent of Minor and a
short touch of minor, but not extents and short touches of both. Which seems
reasonable.

If you're not ringing whole extents, the "strong" pattern of "every change
unique when considered at the higher stage" applies, which is the point of
points 1 and 3. Point 1 also allows for multiple-extent peals at a single 
stage (which is really a degenerate case of point 2, if I had set M>=0 
instead of M>0).

MBD