Theorem dfnot 1361

Description: Given falsum, we can define the negation of a wff ph as the statement that a contradiction 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 1350	. 2 |- -. F.
2		mtt 675	. 2 |- ( -. F. -> ( -. ph <-> ( ph -> F. ) ) )
3	1, 2	ax-mp 5	1 |- ( -. ph <-> ( ph -> F. ) )

Syntax hints:   -. wn 3   -> wi 4   <-> wb 104   F. wfal 1348

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 105  ax-ia2 106  ax-ia3 107  ax-in1 604  ax-in2 605

This theorem depends on definitions:  df-bi 116  df-tru 1346  df-fal 1349

This theorem is referenced by:  inegd  1362  pclem6  1364  alnex  1487  alexim  1633  difin  3359  indifdir  3378  recvguniq  10937  logbgcd1irr  13525  bj-axempty2  13776