let r be real number ; :: thesis: for seq being Real_Sequence st 0 <= r & ( for n being Element of NAT holds seq . n = 1 / (n + r) ) holds
lim seq = 0
let seq be Real_Sequence; :: thesis: ( 0 <= r & ( for n being Element of NAT holds seq . n = 1 / (n + r) ) implies lim seq = 0 )
assume that
A1:
0 <= r
and
A2:
for n being Element of NAT holds seq . n = 1 / (n + r)
; :: thesis: lim seq = 0
A3:
seq is convergent
by A1, A2, Th43;
now let p be
real number ;
:: thesis: ( 0 < p implies ex n being Element of NAT st
for m being Element of NAT st n <= m holds
abs ((seq . m) - 0 ) < p )assume
0 < p
;
:: thesis: ex n being Element of NAT st
for m being Element of NAT st n <= m holds
abs ((seq . m) - 0 ) < pthen A4:
0 < p "
;
consider k1 being
Element of
NAT such that A5:
p " < k1
by Th10;
take n =
k1;
:: thesis: for m being Element of NAT st n <= m holds
abs ((seq . m) - 0 ) < plet m be
Element of
NAT ;
:: thesis: ( n <= m implies abs ((seq . m) - 0 ) < p )assume A6:
n <= m
;
:: thesis: abs ((seq . m) - 0 ) < p
(p " ) + 0 < k1 + r
by A1, A5, XREAL_1:10;
then
1
/ (k1 + r) < 1
/ (p " )
by A4, XREAL_1:78;
then A7:
1
/ (k1 + r) < 1
* ((p " ) " )
by XCMPLX_0:def 9;
n + r <= m + r
by A6, XREAL_1:8;
then
1
/ (m + r) <= 1
/ (n + r)
by A1, A4, A5, XREAL_1:120;
then A9:
1
/ (m + r) < p
by A7, XXREAL_0:2;
A10:
seq . m = 1
/ (m + r)
by A2;
0 <= m
by NAT_1:2;
hence
abs ((seq . m) - 0 ) < p
by A9, A10, A1, ABSVALUE:def 1;
:: thesis: verum end;
hence
lim seq = 0
by A3, SEQ_2:def 7; :: thesis: verum