Theorem pm2.21i

Description: A contradiction implies anything. Inference associated with pm2.21 . Its associated inference is pm2.24ii . (Contributed by NM, 16-Sep-1993)

	Ref	Expression
Hypothesis	pm2.21i.1	$$⊢\neg \phi$$
Assertion	pm2.21i	$$⊢\phi \to \psi$$

Proof

Step	Hyp	Ref	Expression
1		pm2.21i.1	$$⊢\neg \phi$$
2	1	a1i	$$⊢\neg \psi \to \neg \phi$$
3	2	con4i	$$⊢\phi \to \psi$$