I disagree with the way the Springer Encyclopaedia article has been cited. First of all the author of the article is not cited. Second the Russian original is not cited. Only the English translation of the article in Springer version is cited and just editor of the whole thing is mentioned. The true author deserves more mention that the editor. The name of the author can be found on the page in the link (Danilov this time). The fact is that the original Russian mathematical encyclopaedia had the authors listed and that they are preserved by the Springer version. Is only the wikipedia the oblivious/illiterate link in the chain of transfer of knowledge ??