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Theorem nic-idbl 1519
Description: Double the terms. Since doubling is the same as negation, this can be viewed as a contraposition inference. (Contributed by Jeff Hoffman, 17-Nov-2007.) (Proof modification is discouraged.) (New usage is discouraged.)
Hypothesis
Ref Expression
nic-idbl.1
Assertion
Ref Expression
nic-idbl

Proof of Theorem nic-idbl
StepHypRef Expression
1 nic-idbl.1 . . 3
21nic-imp 1508 . 2
31nic-imp 1508 . 2
42, 3nic-ich 1518 1
Colors of variables: wff setvar class
Syntax hints:  -/\wnan 1343
This theorem is referenced by:  nic-luk1  1524
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 185  df-an 371  df-nan 1344
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