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Theorem rb-ax4 1520

Description: The fourth of four axioms in the Russell-Bernays axiom system. (Contributed by Anthony Hart, 13-Aug-2011.) (Proof modification is discouraged.) (New usage is discouraged.)

**Assertion**
Ref	Expression
rb-ax4	$\/$ $\/$

**Proof of Theorem rb-ax4**
Step	Hyp	Ref	Expression
1		pm1.2 499	. . . 4 $\/$
2	1	con3i 127	. . 3 $\/$
3	2	con1i 121	. 2 $\/$
4	3	orri 365	1 $\/$ $\/$

Colors of variables: wff setvar class

Syntax hints:

wn 3 $\/$ wo 357

This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8

This theorem depends on definitions: df-bi 177 df-or 359

This theorem is referenced by: rblem4 1525 rblem5 1526 rblem6 1527 re2luk1 1530 re2luk2 1531 re2luk3 1532

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