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Theorem u4lemnanb 658
Description: Lemma for non-tollens implication study. (Contributed by NM, 16-Dec-1997.)
Assertion
Ref Expression
u4lemnanb ((a4 b)b ) = (ab )

Proof of Theorem u4lemnanb
StepHypRef Expression
1 u4lemob 633 . . 3 ((a4 b) ∪ b) = (ab)
2 oran 87 . . 3 ((a4 b) ∪ b) = ((a4 b)b )
3 oran2 92 . . 3 (ab) = (ab )
41, 2, 33tr2 64 . 2 ((a4 b)b ) = (ab )
54con1 66 1 ((a4 b)b ) = (ab )
Colors of variables: term
Syntax hints:   = wb 1   wn 4  wo 6  wa 7  4 wi4 15
This theorem was proved from axioms:  ax-a1 30  ax-a2 31  ax-a3 32  ax-a4 33  ax-a5 34  ax-r1 35  ax-r2 36  ax-r4 37  ax-r5 38  ax-r3 439
This theorem depends on definitions:  df-b 39  df-a 40  df-t 41  df-f 42  df-i4 47  df-le1 130  df-le2 131  df-c1 132  df-c2 133
This theorem is referenced by: (None)
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