Definition df-ap 8476

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 8571 which says that a number apart from zero has a reciprocal).

The defining characteristics of an apartness are irreflexivity (apirr 8499), symmetry (apsym 8500), and cotransitivity (apcotr 8501). Apartness implies negated equality, as seen at apne 8517, 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 8516).

(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 8475	. 2 class #
2		vx	. . . . . . . . . . 11 setvar x
3	2	cv 1342	. . . . . . . . . 10 class x
4		vr	. . . . . . . . . . . 12 setvar r
5	4	cv 1342	. . . . . . . . . . 11 class r
6		ci 7751	. . . . . . . . . . . 12 class _i
7		vs	. . . . . . . . . . . . 13 setvar s
8	7	cv 1342	. . . . . . . . . . . 12 class s
9		cmul 7754	. . . . . . . . . . . 12 class x.
10	6, 8, 9	co 5841	. . . . . . . . . . 11 class ( _i x. s )
11		caddc 7752	. . . . . . . . . . 11 class +
12	5, 10, 11	co 5841	. . . . . . . . . 10 class ( r + ( _i x. s ) )
13	3, 12	wceq 1343	. . . . . . . . 9 wff x = ( r + ( _i x. s ) )
14		vy	. . . . . . . . . . 11 setvar y
15	14	cv 1342	. . . . . . . . . 10 class y
16		vt	. . . . . . . . . . . 12 setvar t
17	16	cv 1342	. . . . . . . . . . 11 class t
18		vu	. . . . . . . . . . . . 13 setvar u
19	18	cv 1342	. . . . . . . . . . . 12 class u
20	6, 19, 9	co 5841	. . . . . . . . . . 11 class ( _i x. u )
21	17, 20, 11	co 5841	. . . . . . . . . 10 class ( t + ( _i x. u ) )
22	15, 21	wceq 1343	. . . . . . . . 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 8468	. . . . . . . . . 10 class #ℝ
25	5, 17, 24	wbr 3981	. . . . . . . . 9 wff r #ℝ t
26	8, 19, 24	wbr 3981	. . . . . . . . 9 wff s #ℝ u
27	25, 26	wo 698	. . . . . . . 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 7748	. . . . . . 7 class RR
30	28, 18, 29	wrex 2444	. . . . . 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 2444	. . . . 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 2444	. . . 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 2444	. . 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 4041	. 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 1343	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  8481  apreim  8497  aprcl  8540