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Picture 1: Last example on the 'Additional Examples' website for Chapter 11. (Not in the textbook)
Picture 2: p 319, Sweet Reason: A Field Guide to Modern Logic (2010 2 ed) by Henle, Garfield, Tymoczko.
Because the question reveals nothing about whether π and π are true and/or false, do we only assume the most general possibility: that both π and π are true or false? But how does this help to conclude anything about π and π?
The vaccuous truth of universal quantification over an empty set strikes again.
A >--> B because B, being blind, has no accessible worlds, and therefore lacks access to any recourse with which to defend itself. It can supply no information that would keep any proposition in A from being verified.
