Dependency relation

Given the alphabet \Sigma=\{a,b,c\}, a possible dependency relation is D = \{ (a,b),\, (b,a),\, (a,c),\, (c,a),\, (a,a),\, (b,b),\, (c,c) \}, see picture. The corresponding independency is I=\{(b,c),\,(c,b)\}. Then e.g. the symbols b,c are independent of one another, and e.g. a,b are dependent. The string a c b b a is equivalent to a b c b a and to a b b c a, but to no other string. ==References==