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