Theorem 2exnexn

Theorem *11.51 in [WhiteheadRussell] p. 164. (Contributed by Andrew Salmon, 24-May-2011.) (Proof shortened by Wolf Lammen, 25-Sep-2014.)

Conclusion

\( \vdash \exists x \, \forall y \, \varphi \leftrightarrow \neg \forall x \, \exists y \, \neg \varphi \)

Proof

alexn

con2bii _