s/./=&&/g
s/$/;ABCDEFGHIJ/
:1
s/\(.\)\1\(\(=.\1\)*=.\)\(.\)\(.*;.*\1.*\4\)/\1\4\2\1\5/
t1
:
s/\(.\)\(=.\(.\)\(=.\3\)*=\3\)\3/\3\2\1/
t
s/\(=.\)\(.\)\1\(.\)\(.*;.*\3.*\2\)/\1\3\1\2\4/
t
s/=.\|;.*//g