Loop of length 7 starting with a string of length 4
found after enumerating 76 derivations:

.ba.ca
	rule ba -> aabbca at position 0
.aabbca.ca
	rule a ->  at position 5
.aabbc.ca
	rule cc ->  at position 4
.aabb.a
	rule ba -> aabbca at position 3
.aabaabbca.
	rule a ->  at position 3
.aababbca.
	rule b ->  at position 4
.aababca.
	rule b ->  at position 4
.aabaca.