#   a(n(2))
#   Salomma, pp. 12-13.  Attributed to M. Soittola.
#
2:G->a
G->aXBZ
2:BZ->aa
2:Xa->aa
2:Ya->aa
BZ->CYXZ
XA->AYX
YA->CYX
XC->AY
YC->CY
aA->aXXYB
BY->XD
DY->YD
DX->YB
G:10