[r-t] Cover bells

[Richard Smith]

Graham John wrote:

> For example, something like this:
>
> Change-Ringing is the art of ringing a set of tuned bells in a series of
> rows (permutations).  A change is the progression from one row to the next.
> There a number of ways of producing changes.
>
> 1) Call Changes, where...
> 2) Plain Changes, where...
> 3) Methods, where...
> 4) Rule-Based Constructions, where...

I very much like this idea.  And I favour including call 
changes here even if the decisions choose not to allow peals 
of call changes.

> My definition of cover bells, and restriction to one, was as a replacement
> for a CC decision on peals, and consequently a definition of what is, or is
> not a peal. Personally, I feel that we have to limit the term peal (in the
> CC context) to exclude call changes, plain changes and multiple covers, as
> you don't have to be a change ringer to ring a subsequent cover bell, so it
> is no different from ringing a peal of rounds.

If you exclude call changes and plain changes, where do you 
draw the line?  Is a peal allowed to contain a row 
immediately after the same row -- e.g. on 6 bells, is the 
place notation 123456 allowed?  (We included 24 such calls 
in the 1440 at the end of our Dec '03 illegal peal.)

With a small number of these, you are unquestionably still 
in the realm of change ringing.  But if you have too many, 
it becomes whole-pull ringing, or call change ringing, or 
something similar.

You also mention plain changes.  Plain changes on four are 
certainly legal (Double Court or Double Canterbury). 
Depending what exactly you mean by plain changes, and what 
happens to the rule on multiple consecutive blows in one 
place, they may be legal on higher numbers too.

Excluding call changes would be easy -- you simply exclude 
the 'null' change (p.n. 123456 on 6).  And doing so isn't 
going to greatly curtail what can be rung.  But excluding 
plain changes seems much more error-prone.

As to disallowing peals with more than one cover or leading 
bell, I can certainly sympathise with that point of view. 
But that logic only applies to peals where the same bell is 
secondary cover throughout.  I can't see any problems with 
peals of mixed minimus, doubles and minor, for example.  Or 
with a peal of minor and triples rung on eight bells with 
the tenor behind throughout.

One problem that is introduced by cover bells is properly 
understanding what a 'true' peal means.  Philip's 
definitions (as I understand them) mean that all peals of 
covered doubles are false -- they are treated as 6-bell 
peals, but 600 of the rows are never rung.

In the case of peals on more than one stage, the current 
distinction between mixed stages and variable cover is 
important because of its implications on truth.  With mixed 
stages, all that is required is that each extent or 
multi-extent block is true on that number of bells.  In 
variable cover, blocks must be true including the covering 
bell.  Thus, a peal with 6 extents of minor and 6 of doubles 
is true if for the doubles extents either the tenor is 
behind for them all, or each bell is behind for one each, 
but no other possibilities are allowed.

>From this discussion, it appears that the minimal definition 
of a peal is probably "sufficient true changes".  An 
excellent start.  But what does 'sufficient' mean?  What 
does 'true' mean?  And what does 'changes' mean?

Once you start digging into these (especially the definition 
of 'true'), it starts to become apparent how some of the 
complexity of the existing decisions has arisen.

RAS