Theorem nfcvf2

Description: If x and y are distinct, then y is not free in x . Usage of this theorem is discouraged because it depends on ax-13 . See nfcv for a version that replaces the distinctor with a disjoint variable condition, requiring fewer axioms. (Contributed by Mario Carneiro, 5-Dec-2016) (New usage is discouraged.)

	Ref	Expression
Assertion	nfcvf2	$$⊢\neg \forall xx=y\to \underset{\_}{Ⅎ}yx$$

Proof

Step	Hyp	Ref	Expression
1		nfcvf	$$⊢\neg \forall yy=x\to \underset{\_}{Ⅎ}yx$$
2	1	naecoms	$$⊢\neg \forall xx=y\to \underset{\_}{Ⅎ}yx$$