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LGB 2017 edition pg. 321: C<-/->G

Stephanie Turaj
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We recently received the following question from a student. An instructor will respond below. Thanks!

Hello! On page 321 I would like to know how the first inference can be combined with the super rule to create C<-/->G
Jonathan Evans
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Good question! Check out the illustration below followed by a brief explanation:


Consider three scenarios:

  1. What if B is selected? If B is selected, G must be selected (Rule 2) and C must not be selected (Rules 1 & 3 combined).
  2. What if C is selected? If C is selected, B is not selected (Rules 1 & 3) and therefore G is not selected (Rule 4).
  3. What if G is selected? If G is selected, B is selected (Rule 4) and C is not selected (Rules 1 & 3).

Notice in all three scenarios, there is no possible way C and G can be selected together, therefore: C :dblline: G.

In the illustration above, you can see this link between the element in common between both statements, B.

I hope this helps!
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Thank you! Makes sense now.