Loop of length 24 starting with a string of length 6
found after enumerating 5154 derivations:

.cb.bbbb
	rule cb -> acac at position 0
.acac.bbbb
	rule cb -> acac at position 3
.acaacac.bbb
	rule ca -> bb at position 4
.acaabbc.bbb
	rule ab ->  at position 3
.acabc.bbb
	rule ab ->  at position 2
.acc.bbb
	rule cb -> acac at position 2
.acacac.bb
	rule ca -> bb at position 3
.acabbc.bb
	rule ab ->  at position 2
.acbc.bb
	rule cb -> acac at position 1
.aacacc.bb
	rule cb -> acac at position 5
.aacacacac.b
	rule ca -> bb at position 4
.aacabbcac.b
	rule ab ->  at position 3
.aacbcac.b
	rule cb -> acac at position 2
.aaacaccac.b
	rule ca -> bb at position 6
.aaacacbbc.b
	rule cb -> acac at position 5
.aaacaacacbc.b
	rule ca -> bb at position 6
.aaacaabbcbc.b
	rule ab ->  at position 5
.aaacabcbc.b
	rule ab ->  at position 4
.aaaccbc.b
	rule cb -> acac at position 4
.aaacacacc.b
	rule ca -> bb at position 5
.aaacabbcc.b
	rule ab ->  at position 4
.aaacbcc.b
	rule cb -> acac at position 6
.aaacbcacac.
	rule ca -> bb at position 5
.aaacbbbcac.
	rule ca -> bb at position 7
.aaacbbbbbc.