Theorem drnfc1OLD

Description: Obsolete version of drnfc1 as of 22-Sep-2024. (Contributed by Mario Carneiro, 8-Oct-2016) Avoid ax-11 . (Revised by Wolf Lammen, 10-May-2023) (New usage is discouraged.) (Proof modification is discouraged.)

	Ref	Expression
Hypothesis	drnfc1.1	$$⊢\forall xx=y\to A=B$$
Assertion	drnfc1OLD	$$⊢\forall xx=y\to \left(\underset{\_}{Ⅎ}xA\leftrightarrow \underset{\_}{Ⅎ}yB\right)$$

Proof

Step	Hyp	Ref	Expression
1		drnfc1.1	$$⊢\forall xx=y\to A=B$$
2	1	eleq2d	$$⊢\forall xx=y\to \left(w\in A\leftrightarrow w\in B\right)$$
3	2	drnf1	$$⊢\forall xx=y\to \left(Ⅎxw\in A\leftrightarrow Ⅎyw\in B\right)$$
4	3	albidv	$$⊢\forall xx=y\to \left(\forall wℲxw\in A\leftrightarrow \forall wℲyw\in B\right)$$
5		df-nfc	$$⊢\underset{\_}{Ⅎ}xA\leftrightarrow \forall wℲxw\in A$$
6		df-nfc	$$⊢\underset{\_}{Ⅎ}yB\leftrightarrow \forall wℲyw\in B$$
7	4 5 6	3bitr4g	$$⊢\forall xx=y\to \left(\underset{\_}{Ⅎ}xA\leftrightarrow \underset{\_}{Ⅎ}yB\right)$$