let X be set ; for f being PartFunc of REAL,REAL st X c= dom f & f | X is uniformly_continuous holds
f | X is continuous
let f be PartFunc of REAL,REAL; ( X c= dom f & f | X is uniformly_continuous implies f | X is continuous )
assume A1:
X c= dom f
; ( not f | X is uniformly_continuous or f | X is continuous )
assume A2:
f | X is uniformly_continuous
; f | X is continuous
now let x0,
r be
real number ;
( x0 in X & 0 < r implies ex s being real number st
( 0 < s & ( for x1 being real number st x1 in X & abs (x1 - x0) < s holds
abs ((f . x1) - (f . x0)) < r ) ) )assume that A3:
x0 in X
and A4:
0 < r
;
ex s being real number st
( 0 < s & ( for x1 being real number st x1 in X & abs (x1 - x0) < s holds
abs ((f . x1) - (f . x0)) < r ) )A5:
x0 in dom (f | X)
by A1, A3, RELAT_1:62;
r is
Real
by XREAL_0:def 1;
then consider s being
Real such that A6:
0 < s
and A7:
for
x1,
x2 being
Real st
x1 in dom (f | X) &
x2 in dom (f | X) &
abs (x1 - x2) < s holds
abs ((f . x1) - (f . x2)) < r
by A2, A4, Th1;
reconsider s =
s as
real number ;
take s =
s;
( 0 < s & ( for x1 being real number st x1 in X & abs (x1 - x0) < s holds
abs ((f . x1) - (f . x0)) < r ) )thus
0 < s
by A6;
for x1 being real number st x1 in X & abs (x1 - x0) < s holds
abs ((f . x1) - (f . x0)) < rlet x1 be
real number ;
( x1 in X & abs (x1 - x0) < s implies abs ((f . x1) - (f . x0)) < r )assume that A8:
x1 in X
and A9:
abs (x1 - x0) < s
;
abs ((f . x1) - (f . x0)) < r
x1 in dom (f | X)
by A1, A8, RELAT_1:62;
hence
abs ((f . x1) - (f . x0)) < r
by A7, A9, A5;
verum end;
hence
f | X is continuous
by A1, FCONT_1:14; verum