Definition df-ap 7573

Description: Define complex apartness. Definition 6.1 of [Geuvers], p. 17.

Two numbers are considered apart if it is possible to separate them. One common usage is that we can divide by a number if it is apart from zero (see for example recclap 7658 which says that a number apart from zero has a reciprocal).

The defining characteristics of an apartness are irreflexivity (apirr 7596), symmetry (apsym 7597), and cotransitivity (apcotr 7598). Apartness implies negated equality, as seen at apne 7614, and the converse would also follow if we assumed excluded middle.

In addition, apartness of complex numbers is tight, which means that two numbers which are not apart are equal (apti 7613).

(Contributed by Jim Kingdon, 26-Jan-2020.)

Assertion

Ref	Expression
df-ap	|- # = { <. x , y >. | E. r e. RR E. s e. RR E. t e. RR E. u e. RR ( ( x = ( r + ( _i x. s ) ) /\ y = ( t + ( _i x. u ) ) ) /\ ( r #ℝ t \/ s #ℝ u ) ) }

Distinct variable group:   s, r, t, u, x, y

Detailed syntax breakdown of Definition df-ap

Step	Hyp	Ref	Expression
1		cap 7572	. 2 class #
2		vx	. . . . . . . . . . 11 setvar x
3	2	cv 1242	. . . . . . . . . 10 class x
4		vr	. . . . . . . . . . . 12 setvar r
5	4	cv 1242	. . . . . . . . . . 11 class r
6		ci 6891	. . . . . . . . . . . 12 class _i
7		vs	. . . . . . . . . . . . 13 setvar s
8	7	cv 1242	. . . . . . . . . . . 12 class s
9		cmul 6894	. . . . . . . . . . . 12 class x.
10	6, 8, 9	co 5512	. . . . . . . . . . 11 class ( _i x. s )
11		caddc 6892	. . . . . . . . . . 11 class +
12	5, 10, 11	co 5512	. . . . . . . . . 10 class ( r + ( _i x. s ) )
13	3, 12	wceq 1243	. . . . . . . . 9 wff x = ( r + ( _i x. s ) )
14		vy	. . . . . . . . . . 11 setvar y
15	14	cv 1242	. . . . . . . . . 10 class y
16		vt	. . . . . . . . . . . 12 setvar t
17	16	cv 1242	. . . . . . . . . . 11 class t
18		vu	. . . . . . . . . . . . 13 setvar u
19	18	cv 1242	. . . . . . . . . . . 12 class u
20	6, 19, 9	co 5512	. . . . . . . . . . 11 class ( _i x. u )
21	17, 20, 11	co 5512	. . . . . . . . . 10 class ( t + ( _i x. u ) )
22	15, 21	wceq 1243	. . . . . . . . 9 wff y = ( t + ( _i x. u ) )
23	13, 22	wa 97	. . . . . . . 8 wff ( x = ( r + ( _i x. s ) ) /\ y = ( t + ( _i x. u ) ) )
24		creap 7565	. . . . . . . . . 10 class #ℝ
25	5, 17, 24	wbr 3764	. . . . . . . . 9 wff r #ℝ t
26	8, 19, 24	wbr 3764	. . . . . . . . 9 wff s #ℝ u
27	25, 26	wo 629	. . . . . . . 8 wff ( r #ℝ t \/ s #ℝ u )
28	23, 27	wa 97	. . . . . . 7 wff ( ( x = ( r + ( _i x. s ) ) /\ y = ( t + ( _i x. u ) ) ) /\ ( r #ℝ t \/ s #ℝ u ) )
29		cr 6888	. . . . . . 7 class RR
30	28, 18, 29	wrex 2307	. . . . . 6 wff E. u e. RR ( ( x = ( r + ( _i x. s ) ) /\ y = ( t + ( _i x. u ) ) ) /\ ( r #ℝ t \/ s #ℝ u ) )
31	30, 16, 29	wrex 2307	. . . . 5 wff E. t e. RR E. u e. RR ( ( x = ( r + ( _i x. s ) ) /\ y = ( t + ( _i x. u ) ) ) /\ ( r #ℝ t \/ s #ℝ u ) )
32	31, 7, 29	wrex 2307	. . . 4 wff E. s e. RR E. t e. RR E. u e. RR ( ( x = ( r + ( _i x. s ) ) /\ y = ( t + ( _i x. u ) ) ) /\ ( r #ℝ t \/ s #ℝ u ) )
33	32, 4, 29	wrex 2307	. . 3 wff E. r e. RR E. s e. RR E. t e. RR E. u e. RR ( ( x = ( r + ( _i x. s ) ) /\ y = ( t + ( _i x. u ) ) ) /\ ( r #ℝ t \/ s #ℝ u ) )
34	33, 2, 14	copab 3817	. 2 class { <. x , y >. | E. r e. RR E. s e. RR E. t e. RR E. u e. RR ( ( x = ( r + ( _i x. s ) ) /\ y = ( t + ( _i x. u ) ) ) /\ ( r #ℝ t \/ s #ℝ u ) ) }
35	1, 34	wceq 1243	1 wff # = { <. x , y >. | E. r e. RR E. s e. RR E. t e. RR E. u e. RR ( ( x = ( r + ( _i x. s ) ) /\ y = ( t + ( _i x. u ) ) ) /\ ( r #ℝ t \/ s #ℝ u ) ) }

This definition is referenced by:  apreap  7578  apreim  7594