The interest to the trees M23a and
M23b is due to the fact that they
are the only (up to symmetry) trees
edge rotation group of which is Matieu group M23.
This was proved by
-
N.M.Adrianov, Yu.Yu.Kochetkov, A.D.Suvorov
and G.B.Shabat
- Matieu groups and plane trees (in Russian)
-
Fundamental'naya i prikladnaya
matematika, 1(2):377-384, 1995;
- correction: ibid, 2(1):317, 1996
URL of my original Home page is
http://logic.pdmi.ras.ru/~yumat/index.html.
It has a mirror at
http://www.informatik.uni-stuttgart.de/ifi/ti/personen/Matiyasevich/index.html.
All comments can be
e-mailed
to me, Yuri Matiyasevich.