HELP! (Complex 'or' Diagraming)

    • October 27, 2016 at 8:35 am #2810

      Hi Mike!

      I have been having some major trouble with diagraming these rules. I found a post by another user who was having the same issues and perfectly explained why:

      “I’m suddenly encountering some issues — specifically, complex “or” rules. I’m consistently using a different notation for about half of the questions, and I can tell that I’m misunderstanding the underlying logic, but I’m not sure why. Basically, it seems like I keep wanting to diagram: “A-B-C or C-B-A” for rules that should be diagrammed using diagonal lines. like this:

      A \ / A
      B or B
      C / \ C

      I’m not sure how to get this into my head or why/how I’m approaching these questions wrong. I guess the key is that I’m just not understanding how these “diagonal line” diagrams are logically different than simply drawing out “A-B-C or C-B-A.”

      Can someone assist with explaining this? As the user stated above, I also don’t really see a difference in using the diagonal diagram vs. the horizontal diagram. Is there really a difference? Or is it just preference? I want to try and understand fully before moving forward. Any help would be great!


    • October 28, 2016 at 12:15 pm #2811
      Mike Kim

      Hi Tristan —

      Happy to try and help —

      If you saw that other post, I imagine you also saw my response to it — but in case you didn’t, here’s a link and maybe some of that will help —

      In terms of the specific q you brought up —

      wanting to draw something with the horizontal vs with the diagonals —

      let’s try and break down exactly what that means —

      There are two distinct parts of understanding the issue correctly:


      When you have a rule represented:

      “A -B – C”

      what that means, specifically, about the order of those three elements, is that

      A must go before B, which then must go before C.

      When you have a rule represented:

      “A with two diagonals to the right, one going to B, and one going to C”

      what that means, specifically, is that

      A is before both B and C, but we don’t know the order of B and C relative to one another.

      That’s the basic and fundamental difference between those two notations.

      So, if you got the rule “B is after A but before C” it would be correct to diagram it A – B – C

      But if you got the rule “A is before both B and C” it would be incorrect to draw A – B – C..

      Instead, you’d want to draw both B and C to the right of A, and that’s where the diagonal lines come into play.

      Okay, so that’s the first key — and that’s the fundamental difference between notation that goes all in an order and the one with diagonals.


      The second concern is the “or” issue — so, if we are told:

      “These three elements, A, B, and C, must be ordered in one of just two possible ways.

      One way these three elements can be ordered is that A is after both B and C.

      And the other way these elements an be ordered is that A is before both B and C.”

      So, the first option would cause us to draw both B and C to the left of A —

      and the second option would cause us to draw both B and C to the right of A.

      And we’d end up with one of these situations, or the other.

      It would be incorrect to represent the situation with a A – B – C linear chain, because again, nothing in the rules told us that B comes before C.

      So those are the two separate concerns that add up to these complex or scenarios — I probably end up saying the same thing over and over again in the book and my various responses, but I hope hearing it that way helps clear things up a bit more —

      Let me know if you have any follow-up — MK

    • November 6, 2016 at 1:40 pm #2833

      Thanks Mike! This was very helpful !! 🙂

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