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Please could someone clarify about exam 2017.02.15 problem 1.b as following:
The red highlighted step should not be Ⱶ !d&b ?
Since in exercise solution sheet we have as below:
Thanks in advance.
The solution is correct. Where did you get this table from? It is fixed in the new version of the exercise slides:
https://es.cs.uni-kl.de/teaching/vrs/exercises/01-Solutions.pdf (slide 20)
You can also derive this rule on your own as a→b = ¬a ∨ b.
See also lecture slide 96 https://es.cs.uni-kl.de/teaching/vrs/slides/VRS-02-PropLogic-1.pdf