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Metamath Proof Explorer

Theorem nffal

Description: The false constant has no free variables (see nftru ). (Contributed by BJ, 6-May-2019)

Ref Expression
Assertion nffal 
|- F/ x F.

Proof

Step Hyp Ref Expression
1 fal 
 |-  -. F.
2 1 nfnth 
 |-  F/ x F.