2

enter image description here

Is there anyone who could explain to me why these errors occur? It seems to me the rule was used properly.

3

Existential Elimination requires that the witness (a) does not occur in the conclusion or in any undischarged assumptions.

At those points, you have an undischarged assumption that includes a on line 2.


Suggestion: Place the negation introduction subproofs inside each case of the v-elimination subproofs.

|  |_ Ex -Px
|  |  |_ -Pa
|  |  |  |_ Pa & Qa
|  |  |  |  :
1

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.