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Theorem pm2.01 581
Description: Reductio ad absurdum. Theorem *2.01 of [WhiteheadRussell] p. 100. This is valid intuitionistically (in the terminology of Section 1.2 of [Bauer] p. 482 it is a proof of negation not a proof by contradiction); compare with pm2.18dc 788 which only holds for some propositions. (Contributed by Mario Carneiro, 12-May-2015.)
Assertion
Ref Expression
pm2.01  |-  ( (
ph  ->  -.  ph )  ->  -.  ph )

Proof of Theorem pm2.01
StepHypRef Expression
1 ax-in1 579 1  |-  ( (
ph  ->  -.  ph )  ->  -.  ph )
Colors of variables: wff set class
Syntax hints:   -. wn 3    -> wi 4
This theorem was proved from axioms:  ax-in1 579
This theorem is referenced by:  pm2.01d  583  con2d  589  pm2.65i  603  pm4.8  658
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