Theorem nfsbOLD

Description: Obsolete version of nfsb as of 25-Feb-2024. (Contributed by Mario Carneiro, 11-Aug-2016) (New usage is discouraged.) (Proof modification is discouraged.)

	Ref	Expression
Hypothesis	nfsb.1	$$⊢Ⅎz\phi$$
Assertion	nfsbOLD	$$⊢Ⅎz\left[y/x\right]\phi$$

Proof

Step	Hyp	Ref	Expression
1		nfsb.1	$$⊢Ⅎz\phi$$
2		axc16nf	$$⊢\forall zz=y\to Ⅎz\left[y/x\right]\phi$$
3	1	nfsb4	$$⊢\neg \forall zz=y\to Ⅎz\left[y/x\right]\phi$$
4	2 3	pm2.61i	$$⊢Ⅎz\left[y/x\right]\phi$$