Loop of length 18 starting with a string of length 6
found after enumerating 15387 derivations:

.aa.bbbb
	rule aa -> bcac at position 0
.bcac.bbbb
	rule cb -> ba at position 3
.bcaba.bbb
	rule b ->  at position 3
.bcaa.bbb
	rule aa -> bcac at position 2
.bcbcac.bbb
	rule b ->  at position 2
.bccac.bbb
	rule cb -> ba at position 4
.bccaba.bb
	rule b ->  at position 4
.bccaa.bb
	rule aa -> bcac at position 3
.bccbcac.bb
	rule cb -> ba at position 2
.bcbacac.bb
	rule cb -> ba at position 1
.bbaacac.bb
	rule a ->  at position 5
.bbaacc.bb
	rule cb -> ba at position 5
.bbaacba.b
	rule cb -> ba at position 4
.bbaabaa.b
	rule aa -> bcac at position 5
.bbaabbcac.b
	rule a ->  at position 7
.bbaabbcc.b
	rule cb -> ba at position 7
.bbaabbcba.
	rule cb -> ba at position 6
.bbaabbbaa.
	rule aa -> bcac at position 7
.bbaabbbbcac.