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.