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Metamath Proof Explorer

Theorem nfcv

Description: If x is disjoint from A , then x is not free in A . (Contributed by Mario Carneiro, 11-Aug-2016)

Ref Expression
Assertion nfcv 
|- F/_ x A

Proof

Step Hyp Ref Expression
1 nfv 
 |-  F/ x y e. A
2 1 nfci 
 |-  F/_ x A