“…The recent interest was due to Rao, Ruan and Xi [15] on their path breaking solution to a question of David and Semmes, so called the {1, 3, 5} − {1, 4, 5} problem. For the developments and the generalizations, the reader can refer to [2,16,17,21,22,23,24,25] for more details. In particular, in [24], the Lipschitz classification of self-similar sets with exponentially commensurable contraction ratios is characterized in terms of the ideal classes in algebra.…”