let M be non empty Reflexive symmetric triangle MetrStruct ; :: thesis: ( 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 )
:: thesis: ( ( 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
;
:: thesis: 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;
:: thesis: 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;
:: thesis: ( 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
;
:: thesis: A is finite
r / 2
> 0
by A2, XREAL_1:217;
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, TBSP_1:def 1;
defpred S1[
set ,
set ]
means ( $1
in $2 & $2
in G );
A7:
for
x being
set st
x in A holds
ex
y being
set 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
set st
x in A holds
S1[
x,
F . x]
from FUNCT_2:sch 1(A7);
now let x1,
x2 be
set ;
:: thesis: ( x1 in A & x2 in A & F . x1 = F . x2 implies x1 = x2 )assume A11:
(
x1 in A &
x2 in A &
F . x1 = F . x2 )
;
:: thesis: x1 = x2reconsider p1 =
x1,
p2 =
x2 as
Point of
M by A11;
F . x1 in G
by A10, A11;
then consider w being
Point of
M such that A12:
F . x1 = Ball w,
(r / 2)
by A6;
(
p1 in Ball w,
(r / 2) &
p2 in Ball w,
(r / 2) )
by A10, A11, A12;
then
(
dist p1,
w < r / 2 &
dist w,
p2 < r / 2 &
dist p1,
p2 <= (dist p1,w) + (dist w,p2) )
by METRIC_1:4, METRIC_1:12;
then
(
dist p1,
p2 <= (dist p1,w) + (dist w,p2) &
(dist p1,w) + (dist w,p2) < (r / 2) + (r / 2) )
by XREAL_1:10;
then
dist p1,
p2 < (r / 2) + (r / 2)
by XXREAL_0:2;
hence
x1 = x2
by A3, A11;
:: thesis: verum end;
then
(
F is
one-to-one &
dom F = A )
by FUNCT_2:25, FUNCT_2:def 1;
then A13:
A,
rng F are_equipotent
by WELLORD2:def 4;
rng F c= G
hence
A is
finite
by A13, CARD_1:68, A4;
:: thesis: verum
end;
assume A15:
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
; :: thesis: M is totally_bounded
let r be Real; :: according to TBSP_1:def 1 :: thesis: ( 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 A16:
r > 0
; :: thesis: 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 ) ) )
consider A being Subset of M such that
A17:
for p, q being Point of M st p <> q & p in A & q in A holds
dist p,q >= r
and
A18:
for p being Point of M ex q being Point of M st
( q in A & p in Ball q,r )
by A16, Th30;
A19:
A is finite
by A15, A16, A17;
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 } ;
A20:
{ H1(p) where p is Point of M : p in A } is finite
from FRAENKEL:sch 21(A19);
{ 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
; :: thesis: ( 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 ) ) )
union BA = the carrier of M
hence
( BA is finite & union BA = the carrier of M )
by A20; :: thesis: 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; :: thesis: ( not C in BA or ex b1 being Element of the carrier of M st C = Ball b1,r )
assume A24:
C in BA
; :: thesis: ex b1 being Element of the carrier of M st C = Ball b1,r
ex p being Point of M st
( C = H1(p) & p in A )
by A24;
hence
ex b1 being Element of the carrier of M st C = Ball b1,r
; :: thesis: verum