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Theorem nfsb4or 1942
 Description: A variable not free remains so after substitution with a distinct variable. (Contributed by Jim Kingdon, 11-May-2018.)
Hypothesis
Ref Expression
nfsb4or.1
Assertion
Ref Expression
nfsb4or

Proof of Theorem nfsb4or
Dummy variable is distinct from all other variables.
StepHypRef Expression
1 nfsb4or.1 . . 3
21nfsb 1865 . 2
3 sbequ 1763 . 2
42, 3dvelimor 1937 1
 Colors of variables: wff set class Syntax hints:   wo 662  wal 1283  wnf 1390  wsb 1687 This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 104  ax-ia2 105  ax-ia3 106  ax-io 663  ax-5 1377  ax-7 1378  ax-gen 1379  ax-ie1 1423  ax-ie2 1424  ax-8 1436  ax-10 1437  ax-11 1438  ax-i12 1439  ax-bndl 1440  ax-4 1441  ax-17 1460  ax-i9 1464  ax-ial 1468  ax-i5r 1469 This theorem depends on definitions:  df-bi 115  df-nf 1391  df-sb 1688 This theorem is referenced by: (None)
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