Hi LH,
Thanks for the question! I'm going to start by making a side comment about the rules in this game and how they can be diagrammed. In the explanation to this game, which starts on page 308, I spend a lot of time talking about the relationship between A and L, and the fact that because they have opposite necessary conditions, they cannot occur together. That was actually why this drill was created—to further explore that particular idea. I later wrote some blog articles that address how to those rules individually (and which do not focus on the fact that the necessary conditions are opposite (because the two blogs aren't connected directly to this game). So, if you want to explore those rules in more detail, check out the discussion at
http://blog.powerscore.com/lsat/bid/263 ... -Condition and
http://blog.powerscore.com/lsat/bid/263 ... -Condition. Those are not related to your question (which I'll get to in a moment), but it's an interesting point that I had already been planning on adding when I make the 2018 Edition updates for this book
Ok, so on to your question, which asks why I did not diagram out the contrapositives for these rules in the setup. You might notice that early in the book, I tend to draw out contrapositives with greater frequency, and then as the book proceeds, those appear less frequently (and they tend to appear only when the initial rule itself contains all negative terms or is quite unusual). As I note earlier in the book (I don't recall the page number off the top of my head), a statement and its contrapositive are identical in meaning, and are just two different ways of expressing the same idea. As you work more and more with conditional reasoning, seeing contrapositives (CPs) should become second nature, and so much so that you "see" them automatically whenever a conditional statement appears. As such, the value of writing down a CP drops over time, and for me, you should reach a point where it's unnecessary to write them down (which then saves you time) unless you have a situation where writing the CP adds clarity for you.
Now, that said, for some people they really love writing them down and do so at every occasion. that's fine, but understand that you lose small bits of time from doing that, which add up. When I see a statement such as A
B, I know automatically that
B A is also true, and I don't feel the need to write that down. Find your level of comfort with this, and then work towards eliminating the need to write down CPs unless they will really help you see things more clearly.
Please let me know if that helps. Thanks!
