Loop of length 8 starting with a string of length 4
found after enumerating 26 derivations:

.aa.bb
	rule aa -> bab at position 0
.bab.bb
	rule bbb -> aaa at position 2
.baaaa.
	rule aa -> bab at position 1
.bbabaa.
	rule aa -> bab at position 4
.bbabbab.
	rule abb -> b at position 2
.bbbab.
	rule bbb -> aaa at position 0
.aaaab.
	rule aa -> bab at position 2
.aababb.
	rule abb -> b at position 3
.aabb.