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Theorem nfss 3266
 Description: If x is not free in A and B, it is not free in A ⊆ B. (Contributed by NM, 27-Dec-1996.)
Hypotheses
Ref Expression
dfss2f.1 xA
dfss2f.2 xB
Assertion
Ref Expression
nfss x A B

Proof of Theorem nfss
StepHypRef Expression
1 dfss2f.1 . . 3 xA
2 dfss2f.2 . . 3 xB
31, 2dfss3f 3265 . 2 (A Bx A x B)
4 nfra1 2664 . 2 xx A x B
53, 4nfxfr 1570 1 x A B
 Colors of variables: wff setvar class Syntax hints:  Ⅎwnf 1544   ∈ wcel 1710  Ⅎwnfc 2476  ∀wral 2614   ⊆ wss 3257 This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1546  ax-5 1557  ax-17 1616  ax-9 1654  ax-8 1675  ax-6 1729  ax-7 1734  ax-11 1746  ax-12 1925  ax-ext 2334 This theorem depends on definitions:  df-bi 177  df-or 359  df-an 360  df-nan 1288  df-tru 1319  df-ex 1542  df-nf 1545  df-sb 1649  df-clab 2340  df-cleq 2346  df-clel 2349  df-nfc 2478  df-ral 2619  df-v 2861  df-nin 3211  df-compl 3212  df-in 3213  df-ss 3259 This theorem is referenced by:  nfpw  3733  ssiun2s  4010  ssopab2b  4713  nffun  5130  nff  5221  fvmptss  5705
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