Theorem nfdc 1673

Description: If x is not free in ph, it is not free in DECID ph. (Contributed by Jim Kingdon, 11-Mar-2018.)

Hypothesis

Ref	Expression
nfdc.1	|- F/ x ph

Assertion

Ref	Expression
nfdc	|- F/ xDECID ph

Proof of Theorem nfdc

Step	Hyp	Ref	Expression
1		df-dc 836	. 2 |- (DECID ph <-> ( ph \/ -. ph ) )
2		nfdc.1	. . 3 |- F/ x ph
3	2	nfn 1672	. . 3 |- F/ x -. ph
4	2, 3	nfor 1588	. 2 |- F/ x ( ph \/ -. ph )
5	1, 4	nfxfr 1488	1 |- F/ xDECID ph

Syntax hints:   -. wn 3   \/ wo 709  DECID wdc 835   F/wnf 1474

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 106  ax-ia2 107  ax-ia3 108  ax-in1 615  ax-in2 616  ax-io 710  ax-5 1461  ax-gen 1463  ax-ie2 1508  ax-4 1524  ax-ial 1548

This theorem depends on definitions:  df-bi 117  df-dc 836  df-tru 1367  df-fal 1370  df-nf 1475

This theorem is referenced by:  19.32dc  1693  finexdc  6972  ssfirab  7006  opabfi  7008  dcfi  7056  exfzdc  10333  zsupcllemstep  10336  infssuzex  10340  nfsum1  11538  nfsum  11539  nfcprod1  11736  nfcprod  11737  nnwosdc  12231  ctiunctlemudc  12679  iswomninnlem  15780