Theorem wfis2fgOLD

Description: Obsolete proof of wfis2fg as of 17-Nov-2024. (New usage is discouraged.) (Proof modification is discouraged.) (Contributed by Scott Fenton, 11-Feb-2011)

	Ref	Expression
Hypotheses	wfis2fgOLD.1	$$⊢Ⅎy\psi$$
	wfis2fgOLD.2	$$⊢y=z\to \left(\phi \leftrightarrow \psi \right)$$
	wfis2fgOLD.3	$$⊢y\in A\to \left(\forall z\in Pred\left(R,A,y\right)\psi \to \phi \right)$$
Assertion	wfis2fgOLD	$$⊢\left(R\mathrm{We}A\wedge R\mathrm{Se}A\right)\to \forall y\in A\phi$$

Proof

Step	Hyp	Ref	Expression
1		wfis2fgOLD.1	$$⊢Ⅎy\psi$$
2		wfis2fgOLD.2	$$⊢y=z\to \left(\phi \leftrightarrow \psi \right)$$
3		wfis2fgOLD.3	$$⊢y\in A\to \left(\forall z\in Pred\left(R,A,y\right)\psi \to \phi \right)$$
4		sbsbc	$$⊢\left[z/y\right]\phi \leftrightarrow \underset{\dot{}}{[}z/y\underset{\dot{}}{]}\phi$$
5	1 2	sbiev	$$⊢\left[z/y\right]\phi \leftrightarrow \psi$$
6	4 5	bitr3i	$$⊢\underset{\dot{}}{[}z/y\underset{\dot{}}{]}\phi \leftrightarrow \psi$$
7	6	ralbii	$$⊢\forall z\in Pred\left(R,A,y\right)\underset{\dot{}}{[}z/y\underset{\dot{}}{]}\phi \leftrightarrow \forall z\in Pred\left(R,A,y\right)\psi$$
8	7 3	syl5bi	$$⊢y\in A\to \left(\forall z\in Pred\left(R,A,y\right)\underset{\dot{}}{[}z/y\underset{\dot{}}{]}\phi \to \phi \right)$$
9	8	wfisg	$$⊢\left(R\mathrm{We}A\wedge R\mathrm{Se}A\right)\to \forall y\in A\phi$$