444 
Proceedings of the Koyal Society of Edinburgh. [Sess. 
of the groups of three reversals, each may be looked upon as a combination 
of the other two. 
Let S be the portion to which neither twinning operation has been 
applied, S ± that to which T v and S 2 that to which T 2 has been applied, and 
$ 3 that subjected to a combination of both, T B . 
Then [$] = [$J1 ; [ffjr 2 = [SJl ; [^]r 3 = [^ 3 ]l; also T 1 .T 2 = T 2 .T 1 = T B \ 
T B .T 1 = T 1 .T B = T 2 and T 2 . T 3 = T B . T 2 = T r . 
Then and so on. 
The relations between all the different portions can in this manner be 
shown to be those indicated in the following table : — 
Disposition of the structure to 
which the operations are applied 
Resulting disposition of the S l T 1 
S S 1 S 2 S B 
S 1 T, T 0 To 
structure 
To 
T T 
-l O J- O 
To To 
1 
T, 
1 
Operations applied (where 
T = T T\ 
1 3 i l ,i 2 /• 
bUuPI 
See next 
page. 
