Theorem sb4vOLD

Description: Obsolete as of 30-Jul-2023. Use sb6 instead. (Contributed by BJ, 23-Jun-2019) (Proof shortened by Steven Nguyen, 8-Jul-2023) (Proof modification is discouraged.) (New usage is discouraged.)

	Ref	Expression
Assertion	sb4vOLD	$$⊢\left[y/x\right]\phi \to \forall x\left(x=y\to \phi \right)$$

Proof

Step	Hyp	Ref	Expression
1		sb6	$$⊢\left[y/x\right]\phi \leftrightarrow \forall x\left(x=y\to \phi \right)$$
2	1	biimpi	$$⊢\left[y/x\right]\phi \to \forall x\left(x=y\to \phi \right)$$