Loop of length 80 starting with a string of length 21
found after enumerating 5289450 derivations:

.aaaa.aababababbababbab
	rule aaaa -> abbb at position 0
.abbb.aababababbababbab
	rule baab -> aaba at position 3
.abbaaba.abababbababbab
	rule baab -> aaba at position 5
.abbaaaaba.ababbababbab
	rule baab -> aaba at position 7
.abbaaaaaaba.abbababbab
	rule aaaa -> abbb at position 5
.abbaaabbbba.abbababbab
	rule baab -> aaba at position 9
.abbaaabbbaaba.bababbab
	rule baab -> aaba at position 8
.abbaaabbaabaa.bababbab
	rule baab -> aaba at position 10
.abbaaabbaaaaba.ababbab
	rule baab -> aaba at position 12
.abbaaabbaaaaaaba.abbab
	rule aaaa -> abbb at position 10
.abbaaabbaaabbbba.abbab
	rule baab -> aaba at position 14
.abbaaabbaaabbbaaba.bab
	rule baab -> aaba at position 13
.abbaaabbaaabbaabaa.bab
	rule baab -> aaba at position 15
.abbaaabbaaabbaaaaba.ab
	rule baab -> aaba at position 17
.abbaaabbaaabbaaaaaaba.
	rule aaaa -> abbb at position 14
.abbaaabbaaabbaabbbaba.
	rule baab -> aaba at position 12
.abbaaabbaaabaababbaba.
	rule baab -> aaba at position 11
.abbaaabbaaaaabaabbaba.
	rule aaaa -> abbb at position 9
.abbaaabbaabbbbaabbaba.
	rule baab -> aaba at position 13
.abbaaabbaabbbaabababa.
	rule baab -> aaba at position 12
.abbaaabbaabbaabaababa.
	rule baab -> aaba at position 14
.abbaaabbaabbaaaabaaba.
	rule aaaa -> abbb at position 12
.abbaaabbaabbabbbbaaba.
	rule baab -> aaba at position 16
.abbaaabbaabbabbbaabaa.
	rule baab -> aaba at position 15
.abbaaabbaabbabbaabaaa.
	rule baab -> aaba at position 14
.abbaaabbaabbabaabaaaa.
	rule baab -> aaba at position 13
.abbaaabbaabbaaabaaaaa.
	rule aaaa -> abbb at position 17
.abbaaabbaabbaaabaabbb.
	rule baab -> aaba at position 15
.abbaaabbaabbaaaaababb.
	rule aaaa -> abbb at position 13
.abbaaabbaabbaabbbbabb.
	rule baab -> aaba at position 11
.abbaaabbaabaababbbabb.
	rule baab -> aaba at position 10
.abbaaabbaaaabaabbbabb.
	rule baab -> aaba at position 12
.abbaaabbaaaaaababbabb.
	rule aaaa -> abbb at position 9
.abbaaabbaabbbababbabb.
	rule baab -> aaba at position 7
.abbaaabaababbababbabb.
	rule baab -> aaba at position 6
.abbaaaaabaabbababbabb.
	rule aaaa -> abbb at position 4
.abbaabbbbaabbababbabb.
	rule baab -> aaba at position 2
.abaababbbaabbababbabb.
	rule baab -> aaba at position 1
.aaabaabbbaabbababbabb.
	rule baab -> aaba at position 3
.aaaaababbaabbababbabb.
	rule aaaa -> abbb at position 1
.aabbbbabbaabbababbabb.
	rule baab -> aaba at position 8
.aabbbbabaababababbabb.
	rule baab -> aaba at position 7
.aabbbbaaabaabababbabb.
	rule baab -> aaba at position 9
.aabbbbaaaaabaababbabb.
	rule baab -> aaba at position 11
.aabbbbaaaaaaabaabbabb.
	rule aaaa -> abbb at position 9
.aabbbbaaaabbbbaabbabb.
	rule baab -> aaba at position 13
.aabbbbaaaabbbaabababb.
	rule baab -> aaba at position 12
.aabbbbaaaabbaabaababb.
	rule baab -> aaba at position 14
.aabbbbaaaabbaaaabaabb.
	rule baab -> aaba at position 16
.aabbbbaaaabbaaaaaabab.
	rule aaaa -> abbb at position 13
.aabbbbaaaabbaabbbabab.
	rule baab -> aaba at position 11
.aabbbbaaaabaababbabab.
	rule baab -> aaba at position 10
.aabbbbaaaaaabaabbabab.
	rule aaaa -> abbb at position 8
.aabbbbaaabbbbaabbabab.
	rule baab -> aaba at position 12
.aabbbbaaabbbaabababab.
	rule baab -> aaba at position 11
.aabbbbaaabbaabaababab.
	rule baab -> aaba at position 13
.aabbbbaaabbaaaabaabab.
	rule baab -> aaba at position 15
.aabbbbaaabbaaaaaabaab.
	rule aaaa -> abbb at position 12
.aabbbbaaabbaabbbabaab.
	rule baab -> aaba at position 10
.aabbbbaaabaababbabaab.
	rule baab -> aaba at position 9
.aabbbbaaaaabaabbabaab.
	rule aaaa -> abbb at position 7
.aabbbbaabbbbaabbabaab.
	rule baab -> aaba at position 5
.aabbbaababbbaabbabaab.
	rule baab -> aaba at position 4
.aabbaabaabbbaabbabaab.
	rule baab -> aaba at position 6
.aabbaaaababbaabbabaab.
	rule baab -> aaba at position 11
.aabbaaaababaabababaab.
	rule baab -> aaba at position 10
.aabbaaaabaaabaababaab.
	rule baab -> aaba at position 12
.aabbaaaabaaaaabaabaab.
	rule aaaa -> abbb at position 10
.aabbaaaabaabbbbaabaab.
	rule baab -> aaba at position 14
.aabbaaaabaabbbaabaaab.
	rule baab -> aaba at position 13
.aabbaaaabaabbaabaaaab.
	rule baab -> aaba at position 12
.aabbaaaabaabaabaaaaab.
	rule baab -> aaba at position 11
.aabbaaaabaaaabaaaaaab.
	rule aaaa -> abbb at position 15
.aabbaaaabaaaabaabbbab.
	rule baab -> aaba at position 13
.aabbaaaabaaaaaababbab.
	rule aaaa -> abbb at position 10
.aabbaaaabaabbbababbab.
	rule baab -> aaba at position 8
.aabbaaaaaababbababbab.
	rule aaaa -> abbb at position 5
.aabbaabbbababbababbab.
	rule baab -> aaba at position 3
.aabaababbababbababbab.
	rule baab -> aaba at position 2
.aaaabaabbababbababbab.
	rule baab -> aaba at position 4
.aaaaaababababbababbab.