let x0 be Real; for f1, f2 being PartFunc of REAL,REAL st f1 is_left_convergent_in x0 & lim_left (f1,x0) = 0 & ( for r being Real st r < x0 holds
ex g being Real st
( r < g & g < x0 & g in dom (f1 (#) f2) ) ) & ex r being Real st
( 0 < r & f2 | ].(x0 - r),x0.[ is bounded ) holds
( f1 (#) f2 is_left_convergent_in x0 & lim_left ((f1 (#) f2),x0) = 0 )
let f1, f2 be PartFunc of REAL,REAL; ( f1 is_left_convergent_in x0 & lim_left (f1,x0) = 0 & ( for r being Real st r < x0 holds
ex g being Real st
( r < g & g < x0 & g in dom (f1 (#) f2) ) ) & ex r being Real st
( 0 < r & f2 | ].(x0 - r),x0.[ is bounded ) implies ( f1 (#) f2 is_left_convergent_in x0 & lim_left ((f1 (#) f2),x0) = 0 ) )
assume that
A1:
f1 is_left_convergent_in x0
and
A2:
lim_left (f1,x0) = 0
and
A3:
for r being Real st r < x0 holds
ex g being Real st
( r < g & g < x0 & g in dom (f1 (#) f2) )
; ( for r being Real holds
( not 0 < r or not f2 | ].(x0 - r),x0.[ is bounded ) or ( f1 (#) f2 is_left_convergent_in x0 & lim_left ((f1 (#) f2),x0) = 0 ) )
given r being Real such that A4:
0 < r
and
A5:
f2 | ].(x0 - r),x0.[ is bounded
; ( f1 (#) f2 is_left_convergent_in x0 & lim_left ((f1 (#) f2),x0) = 0 )
consider g being real number such that
A6:
for r1 being set st r1 in ].(x0 - r),x0.[ /\ (dom f2) holds
abs (f2 . r1) <= g
by A5, RFUNCT_1:73;
A7:
now set L =
left_open_halfline x0;
let s be
Real_Sequence;
( s is convergent & lim s = x0 & rng s c= (dom (f1 (#) f2)) /\ (left_open_halfline x0) implies ( (f1 (#) f2) /* s is convergent & lim ((f1 (#) f2) /* s) = 0 ) )assume that A8:
s is
convergent
and A9:
lim s = x0
and A10:
rng s c= (dom (f1 (#) f2)) /\ (left_open_halfline x0)
;
( (f1 (#) f2) /* s is convergent & lim ((f1 (#) f2) /* s) = 0 )
x0 - r < x0
by A4, Lm1;
then consider k being
Element of
NAT such that A11:
for
n being
Element of
NAT st
k <= n holds
x0 - r < s . n
by A8, A9, Th1;
A12:
rng (s ^\ k) c= rng s
by VALUED_0:21;
A13:
rng s c= dom (f1 (#) f2)
by A10, Lm2;
dom (f1 (#) f2) = (dom f1) /\ (dom f2)
by A10, Lm2;
then
rng (s ^\ k) c= (dom f1) /\ (dom f2)
by A13, A12, XBOOLE_1:1;
then A14:
(f1 /* (s ^\ k)) (#) (f2 /* (s ^\ k)) =
(f1 (#) f2) /* (s ^\ k)
by RFUNCT_2:8
.=
((f1 (#) f2) /* s) ^\ k
by A13, VALUED_0:27
;
rng s c= (dom f1) /\ (left_open_halfline x0)
by A10, Lm2;
then A15:
rng (s ^\ k) c= (dom f1) /\ (left_open_halfline x0)
by A12, XBOOLE_1:1;
A16:
lim (s ^\ k) = x0
by A8, A9, SEQ_4:20;
then A17:
f1 /* (s ^\ k) is
convergent
by A1, A2, A8, A15, Def7;
rng s c= left_open_halfline x0
by A10, Lm2;
then A18:
rng (s ^\ k) c= left_open_halfline x0
by A12, XBOOLE_1:1;
A19:
rng s c= dom f2
by A10, Lm2;
then A20:
rng (s ^\ k) c= dom f2
by A12, XBOOLE_1:1;
then A24:
f2 /* (s ^\ k) is
bounded
by SEQ_2:3;
A25:
lim (f1 /* (s ^\ k)) = 0
by A1, A2, A8, A16, A15, Def7;
then A26:
(f1 /* (s ^\ k)) (#) (f2 /* (s ^\ k)) is
convergent
by A17, A24, SEQ_2:25;
hence
(f1 (#) f2) /* s is
convergent
by A14, SEQ_4:21;
lim ((f1 (#) f2) /* s) = 0
lim ((f1 /* (s ^\ k)) (#) (f2 /* (s ^\ k))) = 0
by A17, A25, A24, SEQ_2:26;
hence
lim ((f1 (#) f2) /* s) = 0
by A26, A14, SEQ_4:22;
verum end;
hence
f1 (#) f2 is_left_convergent_in x0
by A3, Def1; lim_left ((f1 (#) f2),x0) = 0
hence
lim_left ((f1 (#) f2),x0) = 0
by A7, Def7; verum