Theorem nfs1f 2239

Description: If 𝑥 is not free in 𝜑, it is not free in [𝑦 / 𝑥]𝜑. (Contributed by Mario Carneiro, 11-Aug-2016.)

Hypothesis

Ref	Expression
nfs1f.1	⊢ Ⅎ𝑥𝜑

Assertion

Ref	Expression
nfs1f	⊢ Ⅎ𝑥[𝑦 / 𝑥]𝜑

Proof of Theorem nfs1f

Step	Hyp	Ref	Expression
1		nfs1f.1	. . 3 ⊢ Ⅎ𝑥𝜑
2	1	sbf 2234	. 2 ⊢ ([𝑦 / 𝑥]𝜑 ↔ 𝜑)
3	2, 1	nfxfr 1834	1 ⊢ Ⅎ𝑥[𝑦 / 𝑥]𝜑

Syntax hints:  Ⅎwnf 1765  [wsb 2042

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1777  ax-4 1791  ax-5 1888  ax-6 1947  ax-7 1992  ax-12 2141

This theorem depends on definitions:  df-bi 208  df-ex 1762  df-nf 1766  df-sb 2043

This theorem is referenced by: (None)