let S, T be non empty MetrSpace; for F being Subset of (Funcs ( the carrier of S, the carrier of T)) st TopSpaceMetr S is compact holds
( F is equicontinuous iff for x being Point of S holds F is_equicontinuous_at x )
let F be Subset of (Funcs ( the carrier of S, the carrier of T)); ( TopSpaceMetr S is compact implies ( F is equicontinuous iff for x being Point of S holds F is_equicontinuous_at x ) )
assume A1:
TopSpaceMetr S is compact
; ( F is equicontinuous iff for x being Point of S holds F is_equicontinuous_at x )
hereby ( ( for x being Point of S holds F is_equicontinuous_at x ) implies F is equicontinuous )
assume A2:
F is
equicontinuous
;
for x being Point of S holds F is_equicontinuous_at xthus
for
x being
Point of
S holds
F is_equicontinuous_at x
verumproof
let x0 be
Point of
S;
F is_equicontinuous_at x0let e be
Real;
ASCOLI2:def 2 ( 0 < e implies ex d being Real st
( 0 < d & ( for f being Function of the carrier of S, the carrier of T st f in F holds
for x being Point of S st dist (x,x0) < d holds
dist ((f . x),(f . x0)) < e ) ) )
assume
0 < e
;
ex d being Real st
( 0 < d & ( for f being Function of the carrier of S, the carrier of T st f in F holds
for x being Point of S st dist (x,x0) < d holds
dist ((f . x),(f . x0)) < e ) )
then consider d being
Real such that A3:
(
0 < d & ( for
f being
Function of the
carrier of
S, the
carrier of
T st
f in F holds
for
x1,
x2 being
Point of
S st
dist (
x1,
x2)
< d holds
dist (
(f . x1),
(f . x2))
< e ) )
by A2;
take
d
;
( 0 < d & ( for f being Function of the carrier of S, the carrier of T st f in F holds
for x being Point of S st dist (x,x0) < d holds
dist ((f . x),(f . x0)) < e ) )
thus
0 < d
by A3;
for f being Function of the carrier of S, the carrier of T st f in F holds
for x being Point of S st dist (x,x0) < d holds
dist ((f . x),(f . x0)) < e
let f be
Function of the
carrier of
S, the
carrier of
T;
( f in F implies for x being Point of S st dist (x,x0) < d holds
dist ((f . x),(f . x0)) < e )
assume A4:
f in F
;
for x being Point of S st dist (x,x0) < d holds
dist ((f . x),(f . x0)) < e
let x be
Point of
S;
( dist (x,x0) < d implies dist ((f . x),(f . x0)) < e )
assume
dist (
x,
x0)
< d
;
dist ((f . x),(f . x0)) < e
hence
dist (
(f . x),
(f . x0))
< e
by A3, A4;
verum
end;
end;
assume A5:
for x being Point of S holds F is_equicontinuous_at x
; F is equicontinuous
let e be Real; ASCOLI2:def 3 ( 0 < e implies ex d being Real st
( 0 < d & ( for f being Function of the carrier of S, the carrier of T st f in F holds
for x1, x2 being Point of S st dist (x1,x2) < d holds
dist ((f . x1),(f . x2)) < e ) ) )
assume A6:
0 < e
; ex d being Real st
( 0 < d & ( for f being Function of the carrier of S, the carrier of T st f in F holds
for x1, x2 being Point of S st dist (x1,x2) < d holds
dist ((f . x1),(f . x2)) < e ) )
A7:
[#] (TopSpaceMetr S) is compact
by A1, COMPTS_1:1;
defpred S1[ Element of S, Real] means ( 0 < $2 & ( for f being Function of the carrier of S, the carrier of T st f in F holds
for x being Point of S st dist (x,$1) < $2 holds
dist ((f . x),(f . $1)) < e / 2 ) );
A8:
for x0 being Element of the carrier of S ex d being Element of REAL st S1[x0,d]
consider D being Function of the carrier of S,REAL such that
A10:
for x0 being Element of the carrier of S holds S1[x0,D . x0]
from FUNCT_2:sch 3(A8);
set CV = { (Ball (x0,((D . x0) / 2))) where x0 is Element of S : verum } ;
{ (Ball (x0,((D . x0) / 2))) where x0 is Element of S : verum } c= bool the carrier of (TopSpaceMetr S)
then reconsider CV = { (Ball (x0,((D . x0) / 2))) where x0 is Element of S : verum } as Subset-Family of (TopSpaceMetr S) ;
for P being Subset of (TopSpaceMetr S) st P in CV holds
P is open
then A13:
CV is open
by TOPS_2:def 1;
the carrier of (TopSpaceMetr S) c= union CV
then consider G being Subset-Family of (TopSpaceMetr S) such that
A16:
( G c= CV & G is Cover of [#] (TopSpaceMetr S) & G is finite )
by COMPTS_1:def 4, A7, A13, SETFAM_1:def 11;
defpred S2[ object , object ] means ex x0 being Point of S st
( $2 = x0 & $1 = Ball (x0,((D . x0) / 2)) );
A17:
for Z being object st Z in G holds
ex x0 being object st
( x0 in the carrier of S & S2[Z,x0] )
consider H being Function of G, the carrier of S such that
A19:
for Z being object st Z in G holds
S2[Z,H . Z]
from FUNCT_2:sch 1(A17);
A20:
for Z being object st Z in G holds
Z = Ball ((H /. Z),((D . (H . Z)) / 2))
A23:
dom H = G
by FUNCT_2:def 1;
reconsider D0 = D .: (rng H) as finite Subset of REAL by A16;
A24:
dom D = the carrier of S
by FUNCT_2:def 1;
G <> {}
then consider xx being object such that
A25:
xx in G
by XBOOLE_0:def 1;
rng H <> {}
by A23, A25, FUNCT_1:3;
then consider xx being object such that
A26:
xx in rng H
by XBOOLE_0:def 1;
reconsider xx = xx as Point of S by A26;
A27:
( D0 is bounded_below & lower_bound D0 in D0 )
by SEQ_4:133, A26;
set d0 = lower_bound D0;
consider xx being object such that
A28:
( xx in dom D & xx in rng H & lower_bound D0 = D . xx )
by FUNCT_1:def 6, A27;
reconsider xx = xx as Point of S by A28;
A29:
0 < lower_bound D0
by A28, A10;
take d = (lower_bound D0) / 2; ( 0 < d & ( for f being Function of the carrier of S, the carrier of T st f in F holds
for x1, x2 being Point of S st dist (x1,x2) < d holds
dist ((f . x1),(f . x2)) < e ) )
thus
0 < d
by A29; for f being Function of the carrier of S, the carrier of T st f in F holds
for x1, x2 being Point of S st dist (x1,x2) < d holds
dist ((f . x1),(f . x2)) < e
thus
for f being Function of S,T st f in F holds
for x1, x2 being Point of S st dist (x1,x2) < d holds
dist ((f . x1),(f . x2)) < e
verumproof
let f be
Function of
S,
T;
( f in F implies for x1, x2 being Point of S st dist (x1,x2) < d holds
dist ((f . x1),(f . x2)) < e )
assume A30:
f in F
;
for x1, x2 being Point of S st dist (x1,x2) < d holds
dist ((f . x1),(f . x2)) < e
let x1,
x2 be
Point of
S;
( dist (x1,x2) < d implies dist ((f . x1),(f . x2)) < e )
assume A31:
dist (
x1,
x2)
< d
;
dist ((f . x1),(f . x2)) < e
x1 in union G
by A16, SETFAM_1:def 11, TARSKI:def 3;
then consider X1 being
set such that A32:
(
x1 in X1 &
X1 in G )
by TARSKI:def 4;
A33:
X1 = Ball (
(H /. X1),
((D . (H . X1)) / 2))
by A20, A32;
A34:
(D . (H /. X1)) / 2
< D . (H /. X1)
by A10, XREAL_1:216;
x1 in { y where y is Point of S : dist ((H /. X1),y) < (D . (H . X1)) / 2 }
by A33, A32, METRIC_1:def 14;
then A35:
ex
y being
Point of
S st
(
y = x1 &
dist (
(H /. X1),
y)
< (D . (H . X1)) / 2 )
;
then
dist (
x1,
(H /. X1))
< (D . (H /. X1)) / 2
by A23, PARTFUN1:def 6, A32;
then
dist (
x1,
(H /. X1))
< D . (H /. X1)
by A34, XXREAL_0:2;
then A36:
dist (
(f . x1),
(f . (H /. X1)))
< e / 2
by A10, A30;
A37:
H . X1 in rng H
by A23, A32, FUNCT_1:3;
H /. X1 in dom D
by A24;
then
H . X1 in dom D
by A23, A32, PARTFUN1:def 6;
then
D . (H . X1) in D0
by FUNCT_1:def 6, A37;
then
lower_bound D0 <= D . (H . X1)
by SEQ_4:def 2;
then
(lower_bound D0) / 2
<= (D . (H . X1)) / 2
by XREAL_1:72;
then A38:
dist (
x1,
x2)
< (D . (H . X1)) / 2
by A31, XXREAL_0:2;
A39:
dist (
x2,
(H /. X1))
<= (dist (x1,x2)) + (dist ((H /. X1),x1))
by METRIC_1:4;
(dist (x1,x2)) + (dist ((H /. X1),x1)) < ((D . (H . X1)) / 2) + ((D . (H . X1)) / 2)
by A38, A35, XREAL_1:8;
then
dist (
x2,
(H /. X1))
< D . (H . X1)
by A39, XXREAL_0:2;
then
dist (
x2,
(H /. X1))
< D . (H /. X1)
by PARTFUN1:def 6, A23, A32;
then A40:
dist (
(f . x2),
(f . (H /. X1)))
< e / 2
by A10, A30;
A41:
dist (
(f . x1),
(f . x2))
<= (dist ((f . x1),(f . (H /. X1)))) + (dist ((f . x2),(f . (H /. X1))))
by METRIC_1:4;
(dist ((f . x1),(f . (H /. X1)))) + (dist ((f . x2),(f . (H /. X1)))) < (e / 2) + (e / 2)
by A40, A36, XREAL_1:8;
hence
dist (
(f . x1),
(f . x2))
< e
by A41, XXREAL_0:2;
verum
end;