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Theorem 19.12 1552
Description: Theorem 19.12 of [Margaris] p. 89. Assuming the converse is a mistake sometimes made by beginners! (Contributed by NM, 5-Aug-1993.)
Assertion
Ref Expression
19.12 (xyφyxφ)

Proof of Theorem 19.12
StepHypRef Expression
1 hba1 1430 . . 3 (yφyyφ)
21hbex 1524 . 2 (xyφyxyφ)
3 ax-4 1397 . . 3 (yφφ)
43eximi 1488 . 2 (xyφxφ)
52, 4alrimih 1355 1 (xyφyxφ)
Colors of variables: wff set class
Syntax hints:  wi 4  wal 1240  wex 1378
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 99  ax-ia2 100  ax-ia3 101  ax-5 1333  ax-7 1334  ax-gen 1335  ax-ie1 1379  ax-ie2 1380  ax-4 1397  ax-ial 1424
This theorem depends on definitions:  df-bi 110
This theorem is referenced by:  hbexd  1581  nfexd  1641  cbvexdh  1798
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