Theorem 19.44 1969

Description: Theorem 19.44 of [Margaris] p. 90. See 19.44v 1770 for a version requiring fewer axioms (Contributed by NM, 12-Mar-1993.)

Hypothesis

Ref	Expression
19.44.1

Assertion

Ref	Expression
19.44

Proof of Theorem 19.44

Step	Hyp	Ref	Expression
1		19.43 1693	. 2
2		19.44.1	. . . 4
3	2	19.9 1893	. . 3
4	3	orbi2i 519	. 2
5	1, 4	bitri 249	1

Syntax hints:  <->wb 184  \/wo 368  E.wex 1612  F/wnf 1616

This theorem is referenced by:  eeor  1976

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1618  ax-4 1631  ax-5 1704  ax-6 1747  ax-7 1790  ax-10 1837  ax-12 1854

This theorem depends on definitions:  df-bi 185  df-or 370  df-ex 1613  df-nf 1617