Theorem dfnot 1502

Description: Given falsum F., we can define the negation of a wff ph as the statement that F. follows from assuming ph. (Contributed by Mario Carneiro, 9-Feb-2017.) (Proof shortened by Wolf Lammen, 21-Jul-2019.)

Assertion

Ref	Expression
dfnot	|- ( -. ph <-> ( ph -> F. ) )

Proof of Theorem dfnot

Step	Hyp	Ref	Expression
1		fal 1490	. 2 |- -. F.
2		mtt 354	. 2 |- ( -. F. -> ( -. ph <-> ( ph -> F. ) ) )
3	1, 2	ax-mp 5	1 |- ( -. ph <-> ( ph -> F. ) )

Syntax hints:   -. wn 3   -> wi 4   <-> wb 196   F. wfal 1488

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 197  df-tru 1486  df-fal 1489

This theorem is referenced by:  inegd  1503  bj-godellob  32590