Sequent Calculus

Question

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.

Comments

Why is this question posted in `Study-Organisation (Master)`? It looks like it belongs to a teaching field. Like all recent questions in that category :\

Answer 1

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