let a be real number ; :: thesis: 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;
take
s
; :: thesis: ( 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_1:57;
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();
A3:
( s2 is convergent & lim s2 = 0 )
by A2, SEQ_4:45;
set s3 = s1 + s2;
A5:
s1 + s2 is convergent
by A3, SEQ_2:19;
A6: lim (s1 + s2) =
(s1 . 0 ) + 0
by A3, SEQ_4:59
.=
a
by FUNCOP_1:13
;
A7: lim s1 =
s1 . 0
by SEQ_4:41
.=
a
by FUNCOP_1:13
;
hence
s is convergent
by A5, A6, A7, SEQ_2:33; :: thesis: ( lim s = a & ( for n being Element of NAT holds s . n >= a ) )
thus
lim s = a
by A5, A6, A7, A8, SEQ_2:34; :: thesis: for n being Element of NAT holds s . n >= a
let n be Element of NAT ; :: thesis: s . n >= a
s . n >= s1 . n
by A8;
hence
s . n >= a
by FUNCOP_1:13; :: thesis: verum