Theorem con2bii2

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

	Ref	Expression
Hypothesis	con2bii2.1	$$⊢\phi \leftrightarrow \neg \psi$$
Assertion	con2bii2	$$⊢\neg \phi \leftrightarrow \psi$$

Proof

Step	Hyp	Ref	Expression
1		con2bii2.1	$$⊢\phi \leftrightarrow \neg \psi$$
2	1	con2bii	$$⊢\psi \leftrightarrow \neg \phi$$
3	2	bicomi	$$⊢\neg \phi \leftrightarrow \psi$$