Before revision: For example, the existential closure of the open formula n>2 ∧ xn+yn=zn is the closed formula ∃n ∃x ∃y ∃z (n>2 ∧ xn+yn=zn); the latter formula, when interpreted over the natural numbers , is known to be false by Fermat's Last Theorem.
After revision: For example, the existential closure of the open formula n>2 ∧ xn+yn=zn is the closed formula ∃n ∃x ∃y ∃z (n>2 ∧ xn+yn=zn); the latter formula, when interpreted over the positive integers , is known to be false by Fermat's Last Theorem.