Theorem nfss 3217

Description: If x is not free in A and B, it is not free in A C_ B. (Contributed by NM, 27-Dec-1996.)

Hypotheses

Ref	Expression
dfss2f.1	|- F/_ x A
dfss2f.2	|- F/_ x B

Assertion

Ref	Expression
nfss	|- F/ x A C_ B

Proof of Theorem nfss

Step	Hyp	Ref	Expression
1		dfss2f.1	. . 3 |- F/_ x A
2		dfss2f.2	. . 3 |- F/_ x B
3	1, 2	dfss3f 3216	. 2 |- ( A C_ B <-> A. x e. A x e. B )
4		nfra1 2561	. 2 |- F/ x A. x e. A x e. B
5	3, 4	nfxfr 1520	1 |- F/ x A C_ B

Syntax hints:   F/wnf 1506   e. wcel 2200   F/_wnfc 2359   A.wral 2508   C_ wss 3197

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-io 714  ax-5 1493  ax-7 1494  ax-gen 1495  ax-ie1 1539  ax-ie2 1540  ax-8 1550  ax-10 1551  ax-11 1552  ax-i12 1553  ax-bndl 1555  ax-4 1556  ax-17 1572  ax-i9 1576  ax-ial 1580  ax-i5r 1581  ax-ext 2211

This theorem depends on definitions:  df-bi 117  df-nf 1507  df-sb 1809  df-clab 2216  df-cleq 2222  df-clel 2225  df-nfc 2361  df-ral 2513  df-in 3203  df-ss 3210

This theorem is referenced by:  ssrexf  3286  nfpw  3662  ssiun2s  4009  triun  4195  ssopab2b  4365  nffrfor  4439  tfis  4675  nfrel  4804  nffun  5341  nff  5470  fvmptssdm  5719  ssoprab2b  6061  nfsum1  11867  nfsum  11868  nfcprod1  12065  nfcprod  12066