Loop of length 10 starting with a string of length 6
found after enumerating 87 derivations:

.ab.bbbb
	rule ab -> bbc at position 0
.bbc.bbbb
	rule cb -> bac at position 2
.bbbac.bbb
	rule cb -> bac at position 4
.bbbabac.bb
	rule cb -> bac at position 6
.bbbababac.b
	rule ab -> bbc at position 5
.bbbabbbcac.b
	rule cb -> bac at position 9
.bbbabbbcabac.
	rule ab -> bbc at position 8
.bbbabbbcbbcac.
	rule cb -> bac at position 7
.bbbabbbbacbcac.
	rule cb -> bac at position 9
.bbbabbbbabaccac.
	rule ab -> bbc at position 8
.bbbabbbbbbcaccac.