Theorem sbiedwOLD

Description: Obsolete version of sbiedw as of 28-Jan-2024. (Contributed by Gino Giotto, 10-Jan-2024) (Proof modification is discouraged.) (New usage is discouraged.)

	Ref	Expression
Hypotheses	sbiedw.1	$$⊢Ⅎx\phi$$
	sbiedw.2	$$⊢\phi \to Ⅎx\chi$$
	sbiedw.3	$$⊢\phi \to \left(x=y\to \left(\psi \leftrightarrow \chi \right)\right)$$
Assertion	sbiedwOLD	$$⊢\phi \to \left(\left[y/x\right]\psi \leftrightarrow \chi \right)$$

Proof

Step	Hyp	Ref	Expression
1		sbiedw.1	$$⊢Ⅎx\phi$$
2		sbiedw.2	$$⊢\phi \to Ⅎx\chi$$
3		sbiedw.3	$$⊢\phi \to \left(x=y\to \left(\psi \leftrightarrow \chi \right)\right)$$
4	1	sbrim	$$⊢\left[y/x\right]\left(\phi \to \psi \right)\leftrightarrow \left(\phi \to \left[y/x\right]\psi \right)$$
5	1 2	nfim1	$$⊢Ⅎx\left(\phi \to \chi \right)$$
6	3	com12	$$⊢x=y\to \left(\phi \to \left(\psi \leftrightarrow \chi \right)\right)$$
7	6	pm5.74d	$$⊢x=y\to \left(\left(\phi \to \psi \right)\leftrightarrow \left(\phi \to \chi \right)\right)$$
8	5 7	sbiev	$$⊢\left[y/x\right]\left(\phi \to \psi \right)\leftrightarrow \left(\phi \to \chi \right)$$
9	4 8	bitr3i	$$⊢\left(\phi \to \left[y/x\right]\psi \right)\leftrightarrow \left(\phi \to \chi \right)$$
10	9	pm5.74ri	$$⊢\phi \to \left(\left[y/x\right]\psi \leftrightarrow \chi \right)$$