[r-t] Double extent of major

[Alexander Holroyd]

It seems to me that there is no such restriction.  Any treble dodging 
method should work.  (I have just checked Cambridge).

Taking rows 1,2,5,6,9,10,13,14 of each half lead gives a plain method 
(with lots of jump changes), so these rows form a true extent.  Then each 
of the other rows can be paired up with one of these, with the treble in 
the same place (row 3 with row 1 etc), and the transposition relating the 
pairs with the treble in a given position is always the same.  Therefore 
they form a true extent too.

Ander

> Richard Smith wrote:
>
> I ought to have added that you are restricted to using
> methods that have sensible parity structures -- i.e. so that
> the three changes when the treble is dodging either have +-+
> or -+- parity.  This is exactly the requirement that is
> needed to make a minor method work too.
>
> This more or less rules out double changes (e.g. 1258) other
> than at the division ends -- i.e. when the treble moves
> between dodging positions.  (In principle you could still
> have a double change with, say, a 1234.56.1234 block, but I
> doubt many people would choose to.)
>
> Off the top of my head, the only commonly rung method that
> is affected by this is Cambridge.