The book is good, it has many examples and exercises, it has the results of the exercises at the end with odd numbers and at the same time it also includes material that the reader should know. The problem with the Greek edition is that there are several errors in the translation, specifically even in the comprehension examples, which makes it quite problematic. I suggest that when something doesn't make sense to you, have the English PDF open and check how the statement or problem was correctly translated into Greek.