I cannot solve the following sequent using natural deduction:
∃x∀y P(x,y) ⊢ ∃y∀xP(x,y)
However the familiar example I have no issue in solving:
∃x∀y P(x,y) ⊢ ∀y∃xP(x,y)
I am not sure how it is a valid statement, as it seems to be suggesting that you can swap the positions of 2-place predicates?
Thanks