let a be real number ; ex s being Rational_Sequence st
( s is convergent & lim s = a & ( for n being Element of NAT holds s . n >= a ) )
deffunc H1( Element of NAT ) -> Element of REAL = [/(($1 + 1) * a)\] / ($1 + 1);
consider s being Real_Sequence such that
A1:
for n being Element of NAT holds s . n = H1(n)
from SEQ_1:sch 1();
then reconsider s = s as Rational_Sequence by Def6;
deffunc H2( Element of NAT ) -> Element of REAL = 1 / ($1 + 1);
consider s2 being Real_Sequence such that
A2:
for n being Element of NAT holds s2 . n = H2(n)
from SEQ_1:sch 1();
take
s
; ( s is convergent & lim s = a & ( for n being Element of NAT holds s . n >= a ) )
a in REAL
by XREAL_0:def 1;
then reconsider s1 = NAT --> a as Real_Sequence by FUNCOP_1:45;
set s3 = s1 + s2;
A3:
s2 is convergent
by A2, SEQ_4:30;
then A4:
s1 + s2 is convergent
by SEQ_2:5;
lim s2 = 0
by A2, SEQ_4:30;
then A7: lim (s1 + s2) =
(s1 . 0) + 0
by A3, SEQ_4:42
.=
a
by FUNCOP_1:7
;
A8: lim s1 =
s1 . 0
by SEQ_4:26
.=
a
by FUNCOP_1:7
;
hence
s is convergent
by A4, A7, A5, SEQ_2:19; ( lim s = a & ( for n being Element of NAT holds s . n >= a ) )
thus
lim s = a
by A4, A7, A8, A5, SEQ_2:20; for n being Element of NAT holds s . n >= a
let n be Element of NAT ; s . n >= a
s . n >= s1 . n
by A5;
hence
s . n >= a
by FUNCOP_1:7; verum