let f be PartFunc of REAL,REAL; :: thesis: for g being Real st f is convergent_in+infty holds
( lim_in+infty f = g iff for g1 being Real st 0 < g1 holds
ex r being Real st
for r1 being Real st r < r1 & r1 in dom f holds
abs ((f . r1) - g) < g1 )
let g be Real; :: thesis: ( f is convergent_in+infty implies ( lim_in+infty f = g iff for g1 being Real st 0 < g1 holds
ex r being Real st
for r1 being Real st r < r1 & r1 in dom f holds
abs ((f . r1) - g) < g1 ) )
assume A1: f is convergent_in+infty ; :: thesis: ( lim_in+infty f = g iff for g1 being Real st 0 < g1 holds
ex r being Real st
for r1 being Real st r < r1 & r1 in dom f holds
abs ((f . r1) - g) < g1 )
thus ( lim_in+infty f = g implies for g1 being Real st 0 < g1 holds
ex r being Real st
for r1 being Real st r < r1 & r1 in dom f holds
abs ((f . r1) - g) < g1 ) :: thesis: ( ( for g1 being Real st 0 < g1 holds
ex r being Real st
for r1 being Real st r < r1 & r1 in dom f holds
abs ((f . r1) - g) < g1 ) implies lim_in+infty f = g )

proof

assume A2: lim_in+infty f = g ; :: thesis: for g1 being Real st 0 < g1 holds
ex r being Real st
for r1 being Real st r < r1 & r1 in dom f holds
abs ((f . r1) - g) < g1
given g1 being Real such that A3: 0 < g1 and
A4: for r being Real ex r1 being Real st
( r < r1 & r1 in dom f & abs ((f . r1) - g) >= g1 ) ; :: thesis: contradiction
defpred S₁[ Element of NAT , real number ] means ( $1 < $2 & $2 in dom f & abs ((f . $2) - g) >= g1 );
A5: for n being Element of NAT ex r being Real st S₁[n,r] by A4;
consider s being Real_Sequence such that
A6: for n being Element of NAT holds S₁[n,s . n] from FUNCT_2:sch 3(A5);

now

let x be set ; :: thesis: ( x in rng s implies x in dom f )
assume x in rng s ; :: thesis: x in dom f
then ex n being Element of NAT st s . n = x by FUNCT_2:190;
hence x in dom f by A6; :: thesis: verum

end;

then A7: rng s c= dom f by TARSKI:def 3;

now

let n be Element of NAT ; :: thesis: (incl NAT) . n <= s . n
n < s . n by A6;
hence (incl NAT) . n <= s . n by FUNCT_1:35; :: thesis: verum

end;

then s is divergent_to+infty by Lm4, Th47, Th69;
then ( f /* s is convergent & lim (f /* s) = g ) by A1, A2, A7, Def12;
then consider n being Element of NAT such that
A8: for m being Element of NAT st n <= m holds
abs (((f /* s) . m) - g) < g1 by A3, SEQ_2:def 7;
abs (((f /* s) . n) - g) < g1 by A8;
then abs ((f . (s . n)) - g) < g1 by A7, FUNCT_2:185;
hence contradiction by A6; :: thesis: verum

end;

assume A9: for g1 being Real st 0 < g1 holds
ex r being Real st
for r1 being Real st r < r1 & r1 in dom f holds
abs ((f . r1) - g) < g1 ; :: thesis: lim_in+infty f = g

now

let s be Real_Sequence; :: thesis: ( s is divergent_to+infty & rng s c= dom f implies ( f /* s is convergent & lim (f /* s) = g ) )
assume that
A10: s is divergent_to+infty and
A11: rng s c= dom f ; :: thesis: ( f /* s is convergent & lim (f /* s) = g )

A12: now

let g1 be real number ; :: thesis: ( 0 < g1 implies ex n being Element of NAT st
for m being Element of NAT st n <= m holds
abs (((f /* s) . m) - g) < g1 )
assume A13: 0 < g1 ; :: thesis: ex n being Element of NAT st
for m being Element of NAT st n <= m holds
abs (((f /* s) . m) - g) < g1
g1 is Real by XREAL_0:def 1;
then consider r being Real such that
A14: for r1 being Real st r < r1 & r1 in dom f holds
abs ((f . r1) - g) < g1 by A9, A13;
consider n being Element of NAT such that
A15: for m being Element of NAT st n <= m holds
r < s . m by A10, Def4;
take n = n; :: thesis: for m being Element of NAT st n <= m holds
abs (((f /* s) . m) - g) < g1
let m be Element of NAT ; :: thesis: ( n <= m implies abs (((f /* s) . m) - g) < g1 )
A16: s . m in rng s by VALUED_0:28;
assume n <= m ; :: thesis: abs (((f /* s) . m) - g) < g1
then abs ((f . (s . m)) - g) < g1 by A11, A14, A15, A16;
hence abs (((f /* s) . m) - g) < g1 by A11, FUNCT_2:185; :: thesis: verum

end;

hence f /* s is convergent by SEQ_2:def 6; :: thesis: lim (f /* s) = g
hence lim (f /* s) = g by A12, SEQ_2:def 7; :: thesis: verum

end;

hence lim_in+infty f = g by A1, Def12; :: thesis: verum