Loop of length 20 starting with a string of length 6
found after enumerating 46001 derivations:

.aa.bbbb
	rule aa -> bbcac at position 0
.bbcac.bbbb
	rule cb -> a at position 4
.bbcaa.bbb
	rule aa -> bbcac at position 3
.bbcbbcac.bbb
	rule b ->  at position 3
.bbcbcac.bbb
	rule cb -> a at position 2
.bbacac.bbb
	rule cb -> a at position 5
.bbacaa.bb
	rule aa -> bbcac at position 4
.bbacbbcac.bb
	rule cb -> a at position 3
.bbaabcac.bb
	rule cb -> a at position 7
.bbaabcaa.b
	rule aa -> bbcac at position 6
.bbaabcbbcac.b
	rule b ->  at position 6
.bbaabcbcac.b
	rule cb -> a at position 5
.bbaabacac.b
	rule cb -> a at position 8
.bbaabacaa.
	rule aa -> bbcac at position 7
.bbaabacbbcac.
	rule cb -> a at position 6
.bbaabaabcac.
	rule aa -> bbcac at position 5
.bbaabbbcacbcac.
	rule cb -> a at position 9
.bbaabbbcaacac.
	rule aa -> bbcac at position 8
.bbaabbbcbbcaccac.
	rule cb -> a at position 7
.bbaabbbabcaccac.
	rule a ->  at position 7
.bbaabbbbcaccac.