You will therefore find some references to those inspiring sources throughout this book (Chetverik & Kalinichenko being abbreviated to C&K). I wasn't sure at first whether I wanted to talk about "all existing" lines of this intriguing opening, and discovered in the process there were quite a few, or whether I would sort them out to offer a Black repertoire. I finally decided on the first approach, to give you, dear reader, a broader choice. Among all the lines included in that book, the Four Pawns Attack Classical, covered in the Bonus Lines chapter, is probably the only one where a Black player would need more knowledge in order to be "safe" from a theoretical standpoint.