Among the many works devoted to Copernicus's five hundredth anniversary, the article published here, by the German scientist H.-J. Treder, occupies a special place in the world literature on this subject thanks to its depth of analysis of Copernican concepts. Its author, a member of the Academy of Sciences of the GDR and Director of the Potsdam Astronomical Observatory, is known for his works on Einstein's relativity and gravitation theories. His understanding of Einstein's theory is entirely in accord with the (...) viewpoint advanced in my book The Theory of Space, Time, and Gravitation [Teoriia prostranstva, vremeni i tiagoteniia] , and he cites it repeatedly. In particular, we ascribe major and fundamental significance to the fact that Einstein's gravitation equations require for their solution certain limiting conditions which Einstein's theory, however, does not provide. In order to fill this theoretical gap, it is necessary to introduce certain supplemental hypotheses of a geometrical character concerning space as a whole. Treder very ingeniously demonstrates the similarity between these hypotheses and the ideas of Copernicus. (shrink)