let M be non empty Reflexive symmetric triangle MetrStruct ; ( M is totally_bounded iff for r being Real
for A being Subset of M st r > 0 & ( for p, q being Point of M st p <> q & p in A & q in A holds
dist (p,q) >= r ) holds
A is finite )
thus
( M is totally_bounded implies for r being Real
for A being Subset of M st r > 0 & ( for p, q being Point of M st p <> q & p in A & q in A holds
dist (p,q) >= r ) holds
A is finite )
( ( for r being Real
for A being Subset of M st r > 0 & ( for p, q being Point of M st p <> q & p in A & q in A holds
dist (p,q) >= r ) holds
A is finite ) implies M is totally_bounded )proof
assume A1:
M is
totally_bounded
;
for r being Real
for A being Subset of M st r > 0 & ( for p, q being Point of M st p <> q & p in A & q in A holds
dist (p,q) >= r ) holds
A is finite
let r be
Real;
for A being Subset of M st r > 0 & ( for p, q being Point of M st p <> q & p in A & q in A holds
dist (p,q) >= r ) holds
A is finite let A be
Subset of
M;
( r > 0 & ( for p, q being Point of M st p <> q & p in A & q in A holds
dist (p,q) >= r ) implies A is finite )
assume that A2:
r > 0
and A3:
for
p,
q being
Point of
M st
p <> q &
p in A &
q in A holds
dist (
p,
q)
>= r
;
A is finite
r / 2
> 0
by A2, XREAL_1:215;
then consider G being
Subset-Family of
M such that A4:
G is
finite
and A5:
the
carrier of
M = union G
and A6:
for
C being
Subset of
M st
C in G holds
ex
w being
Point of
M st
C = Ball (
w,
(r / 2))
by A1;
defpred S1[
object ,
object ]
means ex
D2 being
set st
(
D2 = $2 & $1
in D2 & $2
in G );
A7:
for
x being
object st
x in A holds
ex
y being
object st
(
y in bool the
carrier of
M &
S1[
x,
y] )
consider F being
Function of
A,
(bool the carrier of M) such that A10:
for
x being
object st
x in A holds
S1[
x,
F . x]
from FUNCT_2:sch 1(A7);
now for x1, x2 being object st x1 in A & x2 in A & F . x1 = F . x2 holds
x1 = x2let x1,
x2 be
object ;
( x1 in A & x2 in A & F . x1 = F . x2 implies x1 = x2 )assume that A11:
x1 in A
and A12:
x2 in A
and A13:
F . x1 = F . x2
;
x1 = x2reconsider p1 =
x1,
p2 =
x2 as
Point of
M by A11, A12;
A14:
S1[
x1,
F . x1]
by A10, A11;
then
F . x1 in G
;
then consider w being
Point of
M such that A15:
F . x1 = Ball (
w,
(r / 2))
by A6;
p1 in Ball (
w,
(r / 2))
by A15, A14;
then A16:
dist (
p1,
w)
< r / 2
by METRIC_1:11;
A17:
dist (
p1,
p2)
<= (dist (p1,w)) + (dist (w,p2))
by METRIC_1:4;
S1[
x2,
F . x2]
by A10, A12;
then
p2 in Ball (
w,
(r / 2))
by A13, A15;
then
dist (
w,
p2)
< r / 2
by METRIC_1:11;
then
(dist (p1,w)) + (dist (w,p2)) < (r / 2) + (r / 2)
by A16, XREAL_1:8;
then
dist (
p1,
p2)
< (r / 2) + (r / 2)
by A17, XXREAL_0:2;
hence
x1 = x2
by A3, A11, A12;
verum end;
then A18:
F is
one-to-one
by FUNCT_2:19;
A19:
rng F c= G
dom F = A
by FUNCT_2:def 1;
then
A,
rng F are_equipotent
by A18, WELLORD2:def 4;
hence
A is
finite
by A4, A19, CARD_1:38;
verum
end;
assume A22:
for r being Real
for A being Subset of M st r > 0 & ( for p, q being Point of M st p <> q & p in A & q in A holds
dist (p,q) >= r ) holds
A is finite
; M is totally_bounded
let r be Real; TBSP_1:def 1 ( r <= 0 or ex b1 being Element of bool (bool the carrier of M) st
( b1 is finite & the carrier of M = union b1 & ( for b2 being Element of bool the carrier of M holds
( not b2 in b1 or ex b3 being Element of the carrier of M st b2 = Ball (b3,r) ) ) ) )
assume A23:
r > 0
; ex b1 being Element of bool (bool the carrier of M) st
( b1 is finite & the carrier of M = union b1 & ( for b2 being Element of bool the carrier of M holds
( not b2 in b1 or ex b3 being Element of the carrier of M st b2 = Ball (b3,r) ) ) )
reconsider r = r as Real ;
consider A being Subset of M such that
A24:
for p, q being Point of M st p <> q & p in A & q in A holds
dist (p,q) >= r
and
A25:
for p being Point of M ex q being Point of M st
( q in A & p in Ball (q,r) )
by A23, Th29;
deffunc H1( Point of M) -> Element of bool the carrier of M = Ball ($1,r);
set BA = { H1(p) where p is Point of M : p in A } ;
A26:
A is finite
by A22, A23, A24;
A27:
{ H1(p) where p is Point of M : p in A } is finite
from FRAENKEL:sch 21(A26);
{ H1(p) where p is Point of M : p in A } c= bool the carrier of M
then reconsider BA = { H1(p) where p is Point of M : p in A } as Subset-Family of M ;
take
BA
; ( BA is finite & the carrier of M = union BA & ( for b1 being Element of bool the carrier of M holds
( not b1 in BA or ex b2 being Element of the carrier of M st b1 = Ball (b2,r) ) ) )
the carrier of M c= union BA
hence
( BA is finite & union BA = the carrier of M )
by A27, XBOOLE_0:def 10; for b1 being Element of bool the carrier of M holds
( not b1 in BA or ex b2 being Element of the carrier of M st b1 = Ball (b2,r) )
let C be Subset of M; ( not C in BA or ex b1 being Element of the carrier of M st C = Ball (b1,r) )
assume
C in BA
; ex b1 being Element of the carrier of M st C = Ball (b1,r)
then
ex p being Point of M st
( C = H1(p) & p in A )
;
hence
ex b1 being Element of the carrier of M st C = Ball (b1,r)
; verum