Theorem sbequ5

Description: Substitution does not change an identical variable specifier. Usage of this theorem is discouraged because it depends on ax-13 . (Contributed by NM, 15-May-1993) (New usage is discouraged.)

	Ref	Expression
Assertion	sbequ5	$$⊢\left[w/z\right]\forall xx=y\leftrightarrow \forall xx=y$$

Proof

Step	Hyp	Ref	Expression
1		nfae	$$⊢Ⅎz\forall xx=y$$
2	1	sbf	$$⊢\left[w/z\right]\forall xx=y\leftrightarrow \forall xx=y$$