Analyzing And Dissecting Yomi #1, by Josh Silvestri - a Magic: the Gathering Magic Fundamentals article
Let me explain about the layers of yomi. First off, if you haven't read Sirlin's piece on yomi layers or the chapters dealing with yomi in his book, please read this.
For reference, here are the Yomi Layers:
Yomi Layer 0 - The initial play and/or plan (Player A)
Yomi Layer 1 - The opposing counter to the play (Player B)
Yomi Layer 2 - The answer to the counter (Player A)
Yomi Layer 3 - A counter to the counter from Layer 2 (Player B)
Yomi Layer 4 and up then repeats until you run out of viable options and loop back to layer 0.