

October 27, 2016 at 8:35 am #2810tringo335Participant
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: “ABC or CBA” for rules that should be diagrammed using diagonal lines. like this:
A \ / A
B or B
C / \ CI’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 “ABC or CBA.”
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!
Tristan

October 28, 2016 at 12:15 pm #2811Mike KimKeymaster
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:
1.
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.
2.
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 followup — MK

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