Theorem dfnul2 3523

Description: Alternate definition of the empty set. Definition 5.14 of [TakeutiZaring] p. 20. (Contributed by NM, 26-Dec-1996.) Reduce axiom dependencies. (Revised by Steven Nguyen, 3-May-2023.) (Proof shortened by BJ, 23-Sep-2024.)

Assertion

Ref	Expression
dfnul2	|- (/) = { x | -. x = x }

Proof of Theorem dfnul2

Step	Hyp	Ref	Expression
1		dfnul4 3522	. 2 |- (/) = { x | F. }
2		equid 1753	. . . . 5 |- x = x
3	2	notnoti 654	. . . 4 |- -. -. x = x
4	3	bifal 1415	. . 3 |- ( -. x = x <-> F. )
5	4	abbii 2354	. 2 |- { x | -. x = x } = { x | F. }
6	1, 5	eqtr4i 2262	1 |- (/) = { x | -. x = x }

Syntax hints:   -. wn 3   = wceq 1402   F. wfal 1407   {cab 2224   (/)c0 3520

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 106  ax-ia2 107  ax-ia3 108  ax-in1 623  ax-in2 624  ax-5 1500  ax-7 1501  ax-gen 1502  ax-ie1 1546  ax-ie2 1547  ax-8 1557  ax-11 1559  ax-4 1563  ax-17 1579  ax-i9 1583  ax-ial 1587  ax-i5r 1588  ax-ext 2220

This theorem depends on definitions:  df-bi 117  df-tru 1405  df-fal 1408  df-nf 1514  df-sb 1816  df-clab 2225  df-cleq 2231  df-dif 3222  df-nul 3521

This theorem is referenced by:  rab0  3551  iotanul  5348