# [r-t] Bobs only Erin Triples (was: Composition search)

Alan Burlison alan.burlison at gmail.com
Wed Nov 25 11:32:34 UTC 2015

```On 24/11/2015 22:20, Fred Bone wrote:

>> I'm not sure what you mean by "six end" but being able to reduce the
>> number of comparisons sounds good :-)
>
> The method comes in units of six rows, commonly referred to as "sixes".
> The difference between plain and bob is at the transition between two
> sixes, i.e. at the end of one and the start of another: hence "six end".
>
> The point of what Philip says is that for any given four bells in 4th to
> 7th place, the six rows are uniquely determined (ignoring order of
> occurrence). The rows making up the six are alternately odd and even
> permutations (of rounds). The last row will be even, and the six will
> contain all 3 even permutations having the given 4 bells in the given
> places, plus all 3 odd permutations having them swapped in pairs. For
> example, the six ending in xxx4567 will contain all of 1234567, 2314567,
> 3124567, plus 1325476, 2135476 and 3215476 - in some order.

Ah, that makes it clear, thank you.

--
Alan Burlison
--

```