Theorem dfun4 3547

Description: Definition of union in terms of intersection. (Contributed by SF, 12-Jan-2015.)

Assertion

Ref	Expression
dfun4	|- (A u. B) = ∼ ( ∼ A i^i ∼ B)

Proof of Theorem dfun4

Step	Hyp	Ref	Expression
1		dfin5 3546	. . 3 |- ( ∼ A i^i ∼ B) = ∼ ( ∼ ∼ A u. ∼ ∼ B)
2	1	compleqi 3245	. 2 |- ∼ ( ∼ A i^i ∼ B) = ∼ ∼ ( ∼ ∼ A u. ∼ ∼ B)
3		dblcompl 3228	. 2 |- ∼ ∼ ( ∼ ∼ A u. ∼ ∼ B) = ( ∼ ∼ A u. ∼ ∼ B)
4		dblcompl 3228	. . 3 |- ∼ ∼ A = A
5		dblcompl 3228	. . 3 |- ∼ ∼ B = B
6	4, 5	uneq12i 3417	. 2 |- ( ∼ ∼ A u. ∼ ∼ B) = (A u. B)
7	2, 3, 6	3eqtrri 2378	1 |- (A u. B) = ∼ ( ∼ A i^i ∼ B)

Syntax hints:   = wceq 1642   ∼ ccompl 3206   u. cun 3208   i^i cin 3209

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1546  ax-5 1557  ax-17 1616  ax-9 1654  ax-8 1675  ax-6 1729  ax-7 1734  ax-11 1746  ax-12 1925  ax-ext 2334

This theorem depends on definitions:  df-bi 177  df-or 359  df-an 360  df-nan 1288  df-tru 1319  df-ex 1542  df-nf 1545  df-sb 1649  df-clab 2340  df-cleq 2346  df-clel 2349  df-nfc 2479  df-v 2862  df-nin 3212  df-compl 3213  df-in 3214  df-un 3215

This theorem is referenced by:  iinun  3549