Definition df-ap 7682

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 7767 which says that a number apart from zero has a reciprocal).

The defining characteristics of an apartness are irreflexivity (apirr 7705), symmetry (apsym 7706), and cotransitivity (apcotr 7707). Apartness implies negated equality, as seen at apne 7723, 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 7722).

(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 7681	. 2 class #
2		vx	. . . . . . . . . . 11 setvar x
3	2	cv 1283	. . . . . . . . . 10 class x
4		vr	. . . . . . . . . . . 12 setvar r
5	4	cv 1283	. . . . . . . . . . 11 class r
6		ci 6983	. . . . . . . . . . . 12 class _i
7		vs	. . . . . . . . . . . . 13 setvar s
8	7	cv 1283	. . . . . . . . . . . 12 class s
9		cmul 6986	. . . . . . . . . . . 12 class x.
10	6, 8, 9	co 5532	. . . . . . . . . . 11 class ( _i x. s )
11		caddc 6984	. . . . . . . . . . 11 class +
12	5, 10, 11	co 5532	. . . . . . . . . 10 class ( r + ( _i x. s ) )
13	3, 12	wceq 1284	. . . . . . . . 9 wff x = ( r + ( _i x. s ) )
14		vy	. . . . . . . . . . 11 setvar y
15	14	cv 1283	. . . . . . . . . 10 class y
16		vt	. . . . . . . . . . . 12 setvar t
17	16	cv 1283	. . . . . . . . . . 11 class t
18		vu	. . . . . . . . . . . . 13 setvar u
19	18	cv 1283	. . . . . . . . . . . 12 class u
20	6, 19, 9	co 5532	. . . . . . . . . . 11 class ( _i x. u )
21	17, 20, 11	co 5532	. . . . . . . . . 10 class ( t + ( _i x. u ) )
22	15, 21	wceq 1284	. . . . . . . . 9 wff y = ( t + ( _i x. u ) )
23	13, 22	wa 102	. . . . . . . 8 wff ( x = ( r + ( _i x. s ) ) /\ y = ( t + ( _i x. u ) ) )
24		creap 7674	. . . . . . . . . 10 class #ℝ
25	5, 17, 24	wbr 3785	. . . . . . . . 9 wff r #ℝ t
26	8, 19, 24	wbr 3785	. . . . . . . . 9 wff s #ℝ u
27	25, 26	wo 661	. . . . . . . 8 wff ( r #ℝ t \/ s #ℝ u )
28	23, 27	wa 102	. . . . . . 7 wff ( ( x = ( r + ( _i x. s ) ) /\ y = ( t + ( _i x. u ) ) ) /\ ( r #ℝ t \/ s #ℝ u ) )
29		cr 6980	. . . . . . 7 class RR
30	28, 18, 29	wrex 2349	. . . . . 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 2349	. . . . 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 2349	. . . 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 2349	. . 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 3838	. 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 1284	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  7687  apreim  7703