Theorem con1bii2

Description: A contraposition inference. (Contributed by ML, 18-Oct-2020)

	Ref	Expression
Hypothesis	con1bii2.1	$$⊢\neg \phi \leftrightarrow \psi$$
Assertion	con1bii2	$$⊢\phi \leftrightarrow \neg \psi$$

Proof

Step	Hyp	Ref	Expression
1		con1bii2.1	$$⊢\neg \phi \leftrightarrow \psi$$
2	1	con1bii	$$⊢\neg \psi \leftrightarrow \phi$$
3	2	bicomi	$$⊢\phi \leftrightarrow \neg \psi$$