# [r-t] Extension of TDMMs

Sun Aug 15 10:39:00 UTC 2004

```Richard Smith <richard at ex-parrot.com> wrote at 01:55:23 on Sun, 15 Aug
2004
>An example of the more unusual 4n + 6 (n != 4 mod 7) is
>Northumberland S with 2ABCD/2EF.  As the exceptional case
>occurs with 7(4m + 3) working bells, this would suggest a
>head order is -(N+6)/4.  I've not encountered extensions
>which didn't have a fixed lead end before.  Are they common?

I think that the lead head order will always be a linear function of N
(with the exception of the sporadic extensions). Extending by two
stages, the inserted section can cause a bell to stay in the same place
(perhaps after more than one insertion, e.g. Newgate front work), or to
move the same distance as the treble. In general this causes a shift of
0 or +/-1 place bell. The lead head order will then be kN/2 + c. In most
cases it seems that k is even, as the same shift occurs in each half of
the lead, but there are cases (e.g. Single Oxford) where k is odd.
Extending by four stages allows the possibility of +/-1 place bell so

>
>This means that exceptional leads occur whenever (N+6)/4 and
>N-1 are not coprime, or equivalently when n+3 and 4n+5 are
>not coprime.  I can certainly prove that when n=4 (mod 7)
>they are not coprime; however, I cannot prove that they are
>coprime otherwise.  Any ideas?

Put n=m-3, then we have m and 4m-7 not coprime => m=0 (mod 7).

>> >     1  2n + 6 (n != 1, n != 22) ??
>
>Oops. I think n != 22 was mean to read N != 22 (i.e. number
>of bells != 22).

Good - this was worrying me slightly, as I think the modulus ought to be
prime.

--
Regards
Philip