Theorem con2

Contraposition. Theorem *2.03 of [WhiteheadRussell] p. 100. (Contributed by NM, 29-Dec-1992.) (Proof shortened by Wolf Lammen, 12-Feb-2013.)

Conclusion
\( \vdash (\varphi \rightarrow \neg \psi) \rightarrow \psi \rightarrow \neg \varphi \)
Proof
id
con2d _