Loop of length 24 starting with a string of length 8
found after enumerating 1738 derivations:

.ab.bbbbbb
	rule ab -> ca at position 0
.ca.bbbbbb
	rule ab -> ca at position 1
.cca.bbbbb
	rule ab -> ca at position 2
.ccca.bbbb
	rule ab -> ca at position 3
.cccca.bbb
	rule ab -> ca at position 4
.ccccca.bb
	rule ab ->  at position 5
.ccccc.b
	rule cb -> bbba at position 4
.ccccbbba.
	rule cb -> bbba at position 3
.cccbbbabba.
	rule cb -> bbba at position 2
.ccbbbabbabba.
	rule cb -> bbba at position 1
.cbbbabbabbabba.
	rule cb -> bbba at position 0
.bbbabbabbabbabba.
	rule ab -> ca at position 6
.bbbabbcababbabba.
	rule ab -> ca at position 7
.bbbabbccaabbabba.
	rule ab -> ca at position 9
.bbbabbccacababba.
	rule ab ->  at position 10
.bbbabbccacabba.
	rule ab ->  at position 10
.bbbabbccacba.
	rule cb -> bbba at position 9
.bbbabbccabbbaa.
	rule ab -> ca at position 8
.bbbabbcccabbaa.
	rule ab ->  at position 9
.bbbabbcccbaa.
	rule cb -> bbba at position 8
.bbbabbccbbbaaa.
	rule cb -> bbba at position 7
.bbbabbcbbbabbaaa.
	rule cb -> bbba at position 6
.bbbabbbbbabbabbaaa.
	rule ab ->  at position 9
.bbbabbbbbbabbaaa.
	rule ab ->  at position 10
.bbbabbbbbbbaaa.