Definition df-ap 8501

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 8596 which says that a number apart from zero has a reciprocal).

The defining characteristics of an apartness are irreflexivity (apirr 8524), symmetry (apsym 8525), and cotransitivity (apcotr 8526). Apartness implies negated equality, as seen at apne 8542, 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 8541).

(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 8500	. 2 class #
2		vx	. . . . . . . . . . 11 setvar x
3	2	cv 1347	. . . . . . . . . 10 class x
4		vr	. . . . . . . . . . . 12 setvar r
5	4	cv 1347	. . . . . . . . . . 11 class r
6		ci 7776	. . . . . . . . . . . 12 class _i
7		vs	. . . . . . . . . . . . 13 setvar s
8	7	cv 1347	. . . . . . . . . . . 12 class s
9		cmul 7779	. . . . . . . . . . . 12 class x.
10	6, 8, 9	co 5853	. . . . . . . . . . 11 class ( _i x. s )
11		caddc 7777	. . . . . . . . . . 11 class +
12	5, 10, 11	co 5853	. . . . . . . . . 10 class ( r + ( _i x. s ) )
13	3, 12	wceq 1348	. . . . . . . . 9 wff x = ( r + ( _i x. s ) )
14		vy	. . . . . . . . . . 11 setvar y
15	14	cv 1347	. . . . . . . . . 10 class y
16		vt	. . . . . . . . . . . 12 setvar t
17	16	cv 1347	. . . . . . . . . . 11 class t
18		vu	. . . . . . . . . . . . 13 setvar u
19	18	cv 1347	. . . . . . . . . . . 12 class u
20	6, 19, 9	co 5853	. . . . . . . . . . 11 class ( _i x. u )
21	17, 20, 11	co 5853	. . . . . . . . . 10 class ( t + ( _i x. u ) )
22	15, 21	wceq 1348	. . . . . . . . 9 wff y = ( t + ( _i x. u ) )
23	13, 22	wa 103	. . . . . . . 8 wff ( x = ( r + ( _i x. s ) ) /\ y = ( t + ( _i x. u ) ) )
24		creap 8493	. . . . . . . . . 10 class #ℝ
25	5, 17, 24	wbr 3989	. . . . . . . . 9 wff r #ℝ t
26	8, 19, 24	wbr 3989	. . . . . . . . 9 wff s #ℝ u
27	25, 26	wo 703	. . . . . . . 8 wff ( r #ℝ t \/ s #ℝ u )
28	23, 27	wa 103	. . . . . . 7 wff ( ( x = ( r + ( _i x. s ) ) /\ y = ( t + ( _i x. u ) ) ) /\ ( r #ℝ t \/ s #ℝ u ) )
29		cr 7773	. . . . . . 7 class RR
30	28, 18, 29	wrex 2449	. . . . . 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 2449	. . . . 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 2449	. . . 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 2449	. . 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 4049	. 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 1348	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  8506  apreim  8522  aprcl  8565