:: The Series on {B}anach Algebra
:: by Yasunari Shidama
::
:: Copyright (c) 2004-2019 Association of Mizar Users

theorem Th1: :: LOPBAN_3:1
for X being non empty right_complementable add-associative right_zeroed NORMSTR
for seq being sequence of X st ( for n being Nat holds seq . n = 0. X ) holds
for m being Nat holds (Partial_Sums seq) . m = 0. X
proof end;

definition
let X be RealNormSpace;
let seq be sequence of X;
attr seq is summable means :Def1: :: LOPBAN_3:def 1
Partial_Sums seq is convergent ;
end;

:: deftheorem Def1 defines summable LOPBAN_3:def 1 :
for X being RealNormSpace
for seq being sequence of X holds
( seq is summable iff Partial_Sums seq is convergent );

registration
let X be RealNormSpace;
cluster V4() Relation-like NAT -defined the carrier of X -valued Function-like V32( NAT ) V33( NAT , the carrier of X) summable for Element of K32(K33(NAT, the carrier of X));
existence
ex b1 being sequence of X st b1 is summable
proof end;
end;

definition
let X be RealNormSpace;
let seq be sequence of X;
func Sum seq -> Element of X equals :: LOPBAN_3:def 2
lim (Partial_Sums seq);
correctness
coherence
lim (Partial_Sums seq) is Element of X
;
;
end;

:: deftheorem defines Sum LOPBAN_3:def 2 :
for X being RealNormSpace
for seq being sequence of X holds Sum seq = lim (Partial_Sums seq);

definition
let X be RealNormSpace;
let seq be sequence of X;
attr seq is norm_summable means :Def3: :: LOPBAN_3:def 3
||.seq.|| is summable ;
end;

:: deftheorem Def3 defines norm_summable LOPBAN_3:def 3 :
for X being RealNormSpace
for seq being sequence of X holds
( seq is norm_summable iff ||.seq.|| is summable );

theorem Th2: :: LOPBAN_3:2
for X being RealNormSpace
for seq being sequence of X
for m being Nat holds 0 <= ||.seq.|| . m
proof end;

theorem Th3: :: LOPBAN_3:3
for X being RealNormSpace
for x, y, z being Element of X holds ||.(x - y).|| = ||.((x - z) + (z - y)).||
proof end;

theorem Th4: :: LOPBAN_3:4
for X being RealNormSpace
for seq being sequence of X st seq is convergent holds
for s being Real st 0 < s holds
ex n being Nat st
for m being Nat st n <= m holds
||.((seq . m) - (seq . n)).|| < s
proof end;

theorem Th5: :: LOPBAN_3:5
for X being RealNormSpace
for seq being sequence of X holds
( seq is Cauchy_sequence_by_Norm iff for p being Real st p > 0 holds
ex n being Nat st
for m being Nat st n <= m holds
||.((seq . m) - (seq . n)).|| < p )
proof end;

theorem Th6: :: LOPBAN_3:6
for X being RealNormSpace
for seq being sequence of X st ( for n being Nat holds seq . n = 0. X ) holds
for m being Nat holds () . m = 0
proof end;

theorem Th7: :: LOPBAN_3:7
for X being RealNormSpace
for seq, seq1 being sequence of X st seq1 is subsequence of seq & seq is convergent holds
seq1 is convergent
proof end;

theorem Th8: :: LOPBAN_3:8
for X being RealNormSpace
for seq, seq1 being sequence of X st seq1 is subsequence of seq & seq is convergent holds
lim seq1 = lim seq
proof end;

:: Norm Space versions of SEQ_4_33 - SEQ_4_39
theorem :: LOPBAN_3:9
for X being RealNormSpace
for seq, seq1 being sequence of X
for k being Nat st seq is convergent holds
( seq ^\ k is convergent & lim (seq ^\ k) = lim seq ) by ;

theorem Th10: :: LOPBAN_3:10
for X being RealNormSpace
for seq, seq1 being sequence of X st seq is convergent & ex k being Nat st seq = seq1 ^\ k holds
seq1 is convergent
proof end;

theorem Th11: :: LOPBAN_3:11
for X being RealNormSpace
for seq, seq1 being sequence of X st seq is convergent & ex k being Nat st seq = seq1 ^\ k holds
lim seq1 = lim seq
proof end;

theorem Th12: :: LOPBAN_3:12
for X being RealNormSpace
for seq being sequence of X st seq is constant holds
seq is convergent
proof end;

theorem Th13: :: LOPBAN_3:13
for X being RealNormSpace
for seq being sequence of X st ( for n being Nat holds seq . n = 0. X ) holds
seq is norm_summable
proof end;

registration
let X be RealNormSpace;
cluster V4() Relation-like NAT -defined the carrier of X -valued Function-like V32( NAT ) V33( NAT , the carrier of X) norm_summable for Element of K32(K33(NAT, the carrier of X));
existence
ex b1 being sequence of X st b1 is norm_summable
proof end;
end;

:: Norm Space versions of SERIES_1_7 - SERIES_1_16
theorem Th14: :: LOPBAN_3:14
for X being RealNormSpace
for s being sequence of X st s is summable holds
( s is convergent & lim s = 0. X )
proof end;

theorem Th15: :: LOPBAN_3:15
for X being RealNormSpace
for s1, s2 being sequence of X holds () + () = Partial_Sums (s1 + s2)
proof end;

theorem Th16: :: LOPBAN_3:16
for X being RealNormSpace
for s1, s2 being sequence of X holds () - () = Partial_Sums (s1 - s2)
proof end;

registration
let X be RealNormSpace;
let seq be norm_summable sequence of X;
cluster ||.seq.|| -> summable for Real_Sequence;
coherence
for b1 being Real_Sequence st b1 = ||.seq.|| holds
b1 is summable
by Def3;
end;

registration
let X be RealNormSpace;
cluster Function-like V33( NAT , the carrier of X) summable -> convergent for Element of K32(K33(NAT, the carrier of X));
coherence
for b1 being sequence of X st b1 is summable holds
b1 is convergent
by Th14;
end;

theorem Th17: :: LOPBAN_3:17
for X being RealNormSpace
for seq1, seq2 being sequence of X st seq1 is summable & seq2 is summable holds
( seq1 + seq2 is summable & Sum (seq1 + seq2) = (Sum seq1) + (Sum seq2) )
proof end;

theorem Th18: :: LOPBAN_3:18
for X being RealNormSpace
for seq1, seq2 being sequence of X st seq1 is summable & seq2 is summable holds
( seq1 - seq2 is summable & Sum (seq1 - seq2) = (Sum seq1) - (Sum seq2) )
proof end;

registration
let X be RealNormSpace;
let seq1, seq2 be summable sequence of X;
cluster seq1 + seq2 -> summable ;
coherence
seq1 + seq2 is summable
by Th17;
cluster seq1 - seq2 -> summable ;
coherence
seq1 - seq2 is summable
by Th18;
end;

theorem Th19: :: LOPBAN_3:19
for X being RealNormSpace
for seq being sequence of X
for z being Real holds Partial_Sums (z * seq) = z * (Partial_Sums seq)
proof end;

theorem Th20: :: LOPBAN_3:20
for X being RealNormSpace
for seq being summable sequence of X
for z being Real holds
( z * seq is summable & Sum (z * seq) = z * (Sum seq) )
proof end;

registration
let X be RealNormSpace;
let z be Real;
let seq be summable sequence of X;
cluster z * seq -> summable ;
coherence
z * seq is summable
by Th20;
end;

theorem Th21: :: LOPBAN_3:21
for X being RealNormSpace
for s, s1 being sequence of X st ( for n being Nat holds s1 . n = s . 0 ) holds
Partial_Sums (s ^\ 1) = (() ^\ 1) - s1
proof end;

theorem Th22: :: LOPBAN_3:22
for X being RealNormSpace
for s being sequence of X st s is summable holds
for n being Nat holds s ^\ n is summable
proof end;

registration
let X be RealNormSpace;
let seq be summable sequence of X;
let n be Nat;
cluster seq ^\ n -> summable for sequence of X;
coherence
for b1 being sequence of X st b1 = seq ^\ n holds
b1 is summable
by Th22;
end;

theorem Th23: :: LOPBAN_3:23
for X being RealNormSpace
for seq being sequence of X holds
( Partial_Sums ||.seq.|| is bounded_above iff seq is norm_summable )
proof end;

registration
let X be RealNormSpace;
let seq be norm_summable sequence of X;
coherence
for b1 being Real_Sequence st b1 = Partial_Sums ||.seq.|| holds
b1 is bounded_above
by Th23;
end;

theorem Th24: :: LOPBAN_3:24
for X being RealBanachSpace
for seq being sequence of X holds
( seq is summable iff for p being Real st 0 < p holds
ex n being Nat st
for m being Nat st n <= m holds
||.(((Partial_Sums seq) . m) - ((Partial_Sums seq) . n)).|| < p ) by ;

theorem Th25: :: LOPBAN_3:25
for X being RealNormSpace
for s being sequence of X
for n, m being Nat st n <= m holds
||.((() . m) - (() . n)).|| <= |.(( . m) - ( . n)).|
proof end;

theorem Th26: :: LOPBAN_3:26
for X being RealBanachSpace
for seq being sequence of X st seq is norm_summable holds
seq is summable
proof end;

theorem :: LOPBAN_3:27
for X being RealNormSpace
for rseq1 being Real_Sequence
for seq2 being sequence of X st rseq1 is summable & ex m being Nat st
for n being Nat st m <= n holds
||.(seq2 . n).|| <= rseq1 . n holds
seq2 is norm_summable
proof end;

theorem :: LOPBAN_3:28
for X being RealNormSpace
for seq1, seq2 being sequence of X st ( for n being Nat holds
( 0 <= ||.seq1.|| . n & ||.seq1.|| . n <= ||.seq2.|| . n ) ) & seq2 is norm_summable holds
( seq1 is norm_summable & Sum ||.seq1.|| <= Sum ||.seq2.|| ) by SERIES_1:20;

theorem :: LOPBAN_3:29
for X being RealNormSpace
for seq being sequence of X st ( for n being Nat holds ||.seq.|| . n > 0 ) & ex m being Nat st
for n being Nat st n >= m holds
(||.seq.|| . (n + 1)) / (||.seq.|| . n) >= 1 holds
not seq is norm_summable by SERIES_1:27;

theorem :: LOPBAN_3:30
for X being RealNormSpace
for seq being sequence of X
for rseq1 being Real_Sequence st ( for n being Nat holds rseq1 . n = n -root (||.seq.|| . n) ) & rseq1 is convergent & lim rseq1 < 1 holds
seq is norm_summable
proof end;

theorem :: LOPBAN_3:31
for X being RealNormSpace
for seq being sequence of X
for rseq1 being Real_Sequence st ( for n being Nat holds rseq1 . n = n -root (||.seq.|| . n) ) & ex m being Nat st
for n being Nat st m <= n holds
rseq1 . n >= 1 holds
not ||.seq.|| is summable
proof end;

theorem :: LOPBAN_3:32
for X being RealNormSpace
for seq being sequence of X
for rseq1 being Real_Sequence st ( for n being Nat holds rseq1 . n = n -root (||.seq.|| . n) ) & rseq1 is convergent & lim rseq1 > 1 holds
not seq is norm_summable
proof end;

theorem :: LOPBAN_3:33
for X being RealNormSpace
for seq being sequence of X
for rseq1 being Real_Sequence st ||.seq.|| is non-increasing & ( for n being Nat holds rseq1 . n = (2 to_power n) * (||.seq.|| . (2 to_power n)) ) holds
( seq is norm_summable iff rseq1 is summable )
proof end;

theorem :: LOPBAN_3:34
for X being RealNormSpace
for seq being sequence of X
for p being Real st p > 1 & ( for n being Nat st n >= 1 holds
||.seq.|| . n = 1 / (n to_power p) ) holds
seq is norm_summable by SERIES_1:32;

theorem :: LOPBAN_3:35
for X being RealNormSpace
for seq being sequence of X
for p being Real st p <= 1 & ( for n being Nat st n >= 1 holds
||.seq.|| . n = 1 / (n to_power p) ) holds
not seq is norm_summable by SERIES_1:33;

theorem :: LOPBAN_3:36
for X being RealNormSpace
for seq being sequence of X
for rseq1 being Real_Sequence st ( for n being Nat holds
( seq . n <> 0. X & rseq1 . n = (||.seq.|| . (n + 1)) / (||.seq.|| . n) ) ) & rseq1 is convergent & lim rseq1 < 1 holds
seq is norm_summable
proof end;

theorem :: LOPBAN_3:37
for X being RealNormSpace
for seq being sequence of X st ( for n being Nat holds seq . n <> 0. X ) & ex m being Nat st
for n being Nat st n >= m holds
(||.seq.|| . (n + 1)) / (||.seq.|| . n) >= 1 holds
not seq is norm_summable
proof end;

registration
let X be RealBanachSpace;
cluster Function-like V33( NAT , the carrier of X) norm_summable -> summable for Element of K32(K33(NAT, the carrier of X));
coherence
for b1 being sequence of X st b1 is norm_summable holds
b1 is summable
by Th26;
end;

theorem Th38: :: LOPBAN_3:38
for X being Banach_Algebra
for x, y, z being Element of X
for a, b being Real holds
( x + y = y + x & (x + y) + z = x + (y + z) & x + (0. X) = x & ex t being Element of X st x + t = 0. X & (x * y) * z = x * (y * z) & 1 * x = x & 0 * x = 0. X & a * (0. X) = 0. X & (- 1) * x = - x & x * (1. X) = x & (1. X) * x = x & x * (y + z) = (x * y) + (x * z) & (y + z) * x = (y * x) + (z * x) & a * (x * y) = (a * x) * y & a * (x + y) = (a * x) + (a * y) & (a + b) * x = (a * x) + (b * x) & (a * b) * x = a * (b * x) & (a * b) * (x * y) = (a * x) * (b * y) & a * (x * y) = x * (a * y) & (0. X) * x = 0. X & x * (0. X) = 0. X & x * (y - z) = (x * y) - (x * z) & (y - z) * x = (y * x) - (z * x) & (x + y) - z = x + (y - z) & (x - y) + z = x - (y - z) & (x - y) - z = x - (y + z) & x + y = (x - z) + (z + y) & x - y = (x - z) + (z - y) & x = (x - y) + y & x = y - (y - x) & ( = 0 implies x = 0. X ) & ( x = 0. X implies = 0 ) & ||.(a * x).|| = |.a.| * & ||.(x + y).|| <= + & ||.(x * y).|| <= * & ||.(1. X).|| = 1 & X is complete )
proof end;

registration
coherence
for b1 being Banach_Algebra holds b1 is well-unital
proof end;
end;

definition
let X be non empty well-unital associative multLoopStr ;
let v be Element of X;
redefine attr v is invertible means :: LOPBAN_3:def 4
ex w being Element of X st
( v * w = 1. X & w * v = 1. X );
compatibility
( v is invertible iff ex w being Element of X st
( v * w = 1. X & w * v = 1. X ) )
proof end;
end;

:: deftheorem defines invertible LOPBAN_3:def 4 :
for X being non empty well-unital associative multLoopStr
for v being Element of X holds
( v is invertible iff ex w being Element of X st
( v * w = 1. X & w * v = 1. X ) );

definition
let X be non empty multMagma ;
let S be sequence of X;
let a be Element of X;
func a * S -> sequence of X means :: LOPBAN_3:def 5
for n being Nat holds it . n = a * (S . n);
existence
ex b1 being sequence of X st
for n being Nat holds b1 . n = a * (S . n)
proof end;
uniqueness
for b1, b2 being sequence of X st ( for n being Nat holds b1 . n = a * (S . n) ) & ( for n being Nat holds b2 . n = a * (S . n) ) holds
b1 = b2
proof end;
func S * a -> sequence of X means :: LOPBAN_3:def 6
for n being Nat holds it . n = (S . n) * a;
existence
ex b1 being sequence of X st
for n being Nat holds b1 . n = (S . n) * a
proof end;
uniqueness
for b1, b2 being sequence of X st ( for n being Nat holds b1 . n = (S . n) * a ) & ( for n being Nat holds b2 . n = (S . n) * a ) holds
b1 = b2
proof end;
end;

:: deftheorem defines * LOPBAN_3:def 5 :
for X being non empty multMagma
for S being sequence of X
for a being Element of X
for b4 being sequence of X holds
( b4 = a * S iff for n being Nat holds b4 . n = a * (S . n) );

:: deftheorem defines * LOPBAN_3:def 6 :
for X being non empty multMagma
for S being sequence of X
for a being Element of X
for b4 being sequence of X holds
( b4 = S * a iff for n being Nat holds b4 . n = (S . n) * a );

definition
let X be non empty multMagma ;
let seq1, seq2 be sequence of X;
func seq1 * seq2 -> sequence of X means :: LOPBAN_3:def 7
for n being Nat holds it . n = (seq1 . n) * (seq2 . n);
existence
ex b1 being sequence of X st
for n being Nat holds b1 . n = (seq1 . n) * (seq2 . n)
proof end;
uniqueness
for b1, b2 being sequence of X st ( for n being Nat holds b1 . n = (seq1 . n) * (seq2 . n) ) & ( for n being Nat holds b2 . n = (seq1 . n) * (seq2 . n) ) holds
b1 = b2
proof end;
end;

:: deftheorem defines * LOPBAN_3:def 7 :
for X being non empty multMagma
for seq1, seq2, b4 being sequence of X holds
( b4 = seq1 * seq2 iff for n being Nat holds b4 . n = (seq1 . n) * (seq2 . n) );

notation
let X be non empty well-unital associative multLoopStr ;
let x be Element of X;
synonym x " for / x;
end;

definition
let X be non empty well-unital associative multLoopStr ;
let x be Element of X;
assume A1: x is invertible ;
redefine func / x means :Def8: :: LOPBAN_3:def 8
( x * it = 1. X & it * x = 1. X );
compatibility
for b1 being Element of the carrier of X holds
( b1 = x " iff ( x * b1 = 1. X & b1 * x = 1. X ) )
proof end;
end;

:: deftheorem Def8 defines " LOPBAN_3:def 8 :
for X being non empty well-unital associative multLoopStr
for x being Element of X st x is invertible holds
for b3 being Element of the carrier of X holds
( b3 = x " iff ( x * b3 = 1. X & b3 * x = 1. X ) );

definition
let X be Banach_Algebra;
let z be Element of X;
func z GeoSeq -> sequence of X means :Def9: :: LOPBAN_3:def 9
( it . 0 = 1. X & ( for n being Nat holds it . (n + 1) = (it . n) * z ) );
existence
ex b1 being sequence of X st
( b1 . 0 = 1. X & ( for n being Nat holds b1 . (n + 1) = (b1 . n) * z ) )
proof end;
uniqueness
for b1, b2 being sequence of X st b1 . 0 = 1. X & ( for n being Nat holds b1 . (n + 1) = (b1 . n) * z ) & b2 . 0 = 1. X & ( for n being Nat holds b2 . (n + 1) = (b2 . n) * z ) holds
b1 = b2
proof end;
end;

:: deftheorem Def9 defines GeoSeq LOPBAN_3:def 9 :
for X being Banach_Algebra
for z being Element of X
for b3 being sequence of X holds
( b3 = z GeoSeq iff ( b3 . 0 = 1. X & ( for n being Nat holds b3 . (n + 1) = (b3 . n) * z ) ) );

definition
let X be Banach_Algebra;
let z be Element of X;
let n be Nat;
func z #N n -> Element of X equals :: LOPBAN_3:def 10
() . n;
correctness
coherence
() . n is Element of X
;
;
end;

:: deftheorem defines #N LOPBAN_3:def 10 :
for X being Banach_Algebra
for z being Element of X
for n being Nat holds z #N n = () . n;

theorem :: LOPBAN_3:39
for X being Banach_Algebra
for z being Element of X holds z #N 0 = 1. X by Def9;

theorem Th40: :: LOPBAN_3:40
for X being Banach_Algebra
for z being Element of X st < 1 holds
( z GeoSeq is summable & z GeoSeq is norm_summable )
proof end;

theorem :: LOPBAN_3:41
for X being Banach_Algebra
for x being Point of X st ||.((1. X) - x).|| < 1 holds
( ((1. X) - x) GeoSeq is summable & ((1. X) - x) GeoSeq is norm_summable ) by Th40;

Lm1: for X being RealNormSpace
for x being Point of X st ( for e being Real st e > 0 holds
< e ) holds
x = 0. X

proof end;

Lm2: for X being RealNormSpace
for x, y being Point of X st ( for e being Real st e > 0 holds
||.(x - y).|| < e ) holds
x = y

proof end;

Lm3: for X being RealNormSpace
for x, y being Point of X
for seq being Real_Sequence st seq is convergent & lim seq = 0 & ( for n being Nat holds ||.(x - y).|| <= seq . n ) holds
x = y

proof end;

theorem :: LOPBAN_3:42
for X being Banach_Algebra
for x being Point of X st ||.((1. X) - x).|| < 1 holds
( x is invertible & x " = Sum (((1. X) - x) GeoSeq) )
proof end;