Loop of length 9 starting with a string of length 10
found after enumerating 173 derivations:

.aa.bbbabbba
	rule aa -> abb at position 0
.abb.bbbabbba
	rule bbbb -> bbba at position 2
.abbbba.abbba
	rule bbbb -> bbba at position 1
.abbbaa.abbba
	rule aa -> abb at position 5
.abbbaabb.bbba
	rule bbbb -> bbba at position 7
.abbbaabbbba.a
	rule bbbb -> bbba at position 6
.abbbaabbbaa.a
	rule aa -> abb at position 10
.abbbaabbbaabb.
	rule aa -> abb at position 9
.abbbaabbbabbbb.
	rule bbbb -> bbba at position 10
.abbbaabbbabbba.