I have tried to add a double negation to the left hand side and then swap the existential quantifiers, which gives:
¬¬∀x ∃y ∀z P(x, y, z) ⇔
¬∃x ¬∃y ∀z P(x, y, z)
This, I thought, means I can swap the x and y around because you can swap two of the same quantifiers around. This gives:
¬∃y ¬∃x ∀z P(x, y, z)
but when pushing the negation back to the left I get:
∀y ∃x ∀z P(x, y, z)
which means that ∀x ∃y ⇔ ∀y ∃x. Is this true, or even helpful to solving the question?
Take $P(x,y,z) = x<y$ for a simple counterexample.