:: BHSP_3 semantic presentation

deffunc H1( RealUnitarySpace) -> M3(the carrier of a1) = 0. a1;

definition
let c1 be RealUnitarySpace;
let c2 be sequence of c1;
attr a2 is Cauchy means :E1: :: BHSP_3:def 1
for b1 being Real holds
not ( b1 > 0 & ( for b2 being Nat holds
ex b3, b4 being Nat st
( b3 >= b2 & b4 >= b2 & not dist (a2 . b3),(a2 . b4) < b1 ) ) );
end;

:: deftheorem E1 defines Cauchy BHSP_3:def 1 :
for b1 being RealUnitarySpace
for b2 being sequence of b1 holds
( b2 is Cauchy iff for b3 being Real holds
not ( b3 > 0 & ( for b4 being Nat holds
ex b5, b6 being Nat st
( b5 >= b4 & b6 >= b4 & not dist (b2 . b5),(b2 . b6) < b3 ) ) ) );

notation
let c1 be RealUnitarySpace;
let c2 be sequence of c1;
synonym c2 is_Cauchy_sequence for Cauchy c2;
end;

theorem :: BHSP_3:1
for b1 being RealUnitarySpace
for b2 being sequence of b1 holds
( b2 is constant implies b2 is_Cauchy_sequence )
proof
let c1 be RealUnitarySpace;
let c2 be sequence of c1;
assume E2: c2 is constant ;
let c3 be Real; :: according to BHSP_3:def 1
assume E3: c3 > 0 ;
take c4 = 0;
let c5, c6 be Nat;
assume ( c5 >= c4 & c6 >= c4 ) ;
dist (c2 . c5),(c2 . c6) = dist (c2 . c5),(c2 . c5) by E2, BHSP_1:70
.= 0 by BHSP_1:41 ;
hence dist (c2 . c5),(c2 . c6) < c3 by E3;
end;

theorem :: BHSP_3:2
for b1 being RealUnitarySpace
for b2 being sequence of b1 holds
( b2 is_Cauchy_sequence iff for b3 being Real holds
not ( b3 > 0 & ( for b4 being Nat holds
ex b5, b6 being Nat st
( b5 >= b4 & b6 >= b4 & not ||.((b2 . b5) - (b2 . b6)).|| < b3 ) ) ) )
proof
let c1 be RealUnitarySpace;
let c2 be sequence of c1;
thus ( c2 is_Cauchy_sequence implies for b1 being Real holds
not ( b1 > 0 & ( for b2 being Nat holds
ex b3, b4 being Nat st
( b3 >= b2 & b4 >= b2 & not ||.((c2 . b3) - (c2 . b4)).|| < b1 ) ) ) )
proof
assume E2: c2 is_Cauchy_sequence ;
let c3 be Real;
assume c3 > 0 ;
then consider c4 being Nat such that
E3: for b1, b2 being Nat holds
not ( b1 >= c4 & b2 >= c4 & not dist (c2 . b1),(c2 . b2) < c3 ) by E2, E1;
take c5 = c4;
let c6, c7 be Nat;
assume ( c6 >= c5 & c7 >= c5 ) ;
then dist (c2 . c6),(c2 . c7) < c3 by E3;
hence ||.((c2 . c6) - (c2 . c7)).|| < c3 by BHSP_1:def 5;
end;
( ( for b1 being Real holds
not ( b1 > 0 & ( for b2 being Nat holds
ex b3, b4 being Nat st
( b3 >= b2 & b4 >= b2 & not ||.((c2 . b3) - (c2 . b4)).|| < b1 ) ) ) ) implies c2 is_Cauchy_sequence )
proof
assume E2: for b1 being Real holds
not ( b1 > 0 & ( for b2 being Nat holds
ex b3, b4 being Nat st
( b3 >= b2 & b4 >= b2 & not ||.((c2 . b3) - (c2 . b4)).|| < b1 ) ) ) ;
let c3 be Real; :: according to BHSP_3:def 1
assume c3 > 0 ;
then consider c4 being Nat such that
E3: for b1, b2 being Nat holds
not ( b1 >= c4 & b2 >= c4 & not ||.((c2 . b1) - (c2 . b2)).|| < c3 ) by E2;
take c5 = c4;
let c6, c7 be Nat;
assume ( c6 >= c5 & c7 >= c5 ) ;
then ||.((c2 . c6) - (c2 . c7)).|| < c3 by E3;
hence dist (c2 . c6),(c2 . c7) < c3 by BHSP_1:def 5;
end;
hence ( ( for b1 being Real holds
not ( b1 > 0 & ( for b2 being Nat holds
ex b3, b4 being Nat st
( b3 >= b2 & b4 >= b2 & not ||.((c2 . b3) - (c2 . b4)).|| < b1 ) ) ) ) implies c2 is_Cauchy_sequence ) ;
end;

theorem :: BHSP_3:3
for b1 being RealUnitarySpace
for b2, b3 being sequence of b1 holds
( ( b2 is_Cauchy_sequence & b3 is_Cauchy_sequence ) implies ( b2 + b3 is_Cauchy_sequence ) )
proof
let c1 be RealUnitarySpace;
let c2, c3 be sequence of c1;
assume that
E2: c2 is_Cauchy_sequence and
E3: c3 is_Cauchy_sequence ;
let c4 be Real; :: according to BHSP_3:def 1
assume c4 > 0 ;
then E4: c4 / 2 > 0 by SEQ_2:3;
then consider c5 being Nat such that
E5: for b1, b2 being Nat holds
not ( b1 >= c5 & b2 >= c5 & not dist (c2 . b1),(c2 . b2) < c4 / 2 ) by E2, E1;
consider c6 being Nat such that
E6: for b1, b2 being Nat holds
not ( b1 >= c6 & b2 >= c6 & not dist (c3 . b1),(c3 . b2) < c4 / 2 ) by E3, E4, E1;
take c7 = c5 + c6;
let c8, c9 be Nat;
assume E7: ( c8 >= c7 & c9 >= c7 ) ;
c5 + c6 >= c5 by NAT_1:37;
then ( c8 >= c5 & c9 >= c5 ) by E7, XXREAL_0:2;
then E8: dist (c2 . c8),(c2 . c9) < c4 / 2 by E5;
c7 >= c6 by NAT_1:37;
then ( c8 >= c6 & c9 >= c6 ) by E7, XXREAL_0:2;
then dist (c3 . c8),(c3 . c9) < c4 / 2 by E6;
then E9: (dist (c2 . c8),(c2 . c9)) + (dist (c3 . c8),(c3 . c9)) < (c4 / 2) + (c4 / 2) by E8, XREAL_1:10;
dist ((c2 + c3) . c8),((c2 + c3) . c9) = dist ((c2 . c8) + (c3 . c8)),((c2 + c3) . c9) by NORMSP_1:def 5
.= dist ((c2 . c8) + (c3 . c8)),((c2 . c9) + (c3 . c9)) by NORMSP_1:def 5 ;
then dist ((c2 + c3) . c8),((c2 + c3) . c9) <= (dist (c2 . c8),(c2 . c9)) + (dist (c3 . c8),(c3 . c9)) by BHSP_1:47;
hence dist ((c2 + c3) . c8),((c2 + c3) . c9) < c4 by E9, XXREAL_0:2;
end;

theorem :: BHSP_3:4
for b1 being RealUnitarySpace
for b2, b3 being sequence of b1 holds
( ( b2 is_Cauchy_sequence & b3 is_Cauchy_sequence ) implies ( b2 - b3 is_Cauchy_sequence ) )
proof
let c1 be RealUnitarySpace;
let c2, c3 be sequence of c1;
assume that
E2: c2 is_Cauchy_sequence and
E3: c3 is_Cauchy_sequence ;
let c4 be Real; :: according to BHSP_3:def 1
assume c4 > 0 ;
then E4: c4 / 2 > 0 by SEQ_2:3;
then consider c5 being Nat such that
E5: for b1, b2 being Nat holds
not ( b1 >= c5 & b2 >= c5 & not dist (c2 . b1),(c2 . b2) < c4 / 2 ) by E2, E1;
consider c6 being Nat such that
E6: for b1, b2 being Nat holds
not ( b1 >= c6 & b2 >= c6 & not dist (c3 . b1),(c3 . b2) < c4 / 2 ) by E3, E4, E1;
take c7 = c5 + c6;
let c8, c9 be Nat;
assume E7: ( c8 >= c7 & c9 >= c7 ) ;
c5 + c6 >= c5 by NAT_1:37;
then ( c8 >= c5 & c9 >= c5 ) by E7, XXREAL_0:2;
then E8: dist (c2 . c8),(c2 . c9) < c4 / 2 by E5;
c7 >= c6 by NAT_1:37;
then ( c8 >= c6 & c9 >= c6 ) by E7, XXREAL_0:2;
then dist (c3 . c8),(c3 . c9) < c4 / 2 by E6;
then E9: (dist (c2 . c8),(c2 . c9)) + (dist (c3 . c8),(c3 . c9)) < (c4 / 2) + (c4 / 2) by E8, XREAL_1:10;
dist ((c2 - c3) . c8),((c2 - c3) . c9) = dist ((c2 . c8) - (c3 . c8)),((c2 - c3) . c9) by NORMSP_1:def 6
.= dist ((c2 . c8) - (c3 . c8)),((c2 . c9) - (c3 . c9)) by NORMSP_1:def 6 ;
then dist ((c2 - c3) . c8),((c2 - c3) . c9) <= (dist (c2 . c8),(c2 . c9)) + (dist (c3 . c8),(c3 . c9)) by BHSP_1:48;
hence dist ((c2 - c3) . c8),((c2 - c3) . c9) < c4 by E9, XXREAL_0:2;
end;

theorem E2: :: BHSP_3:5
for b1 being RealUnitarySpace
for b2 being Real
for b3 being sequence of b1 holds
( b3 is_Cauchy_sequence implies b2 * b3 is_Cauchy_sequence )
proof
let c1 be RealUnitarySpace;
let c2 be Real;
let c3 be sequence of c1;
assume E3: c3 is_Cauchy_sequence ;
E4: now
assume E5: c2 = 0 ;
let c4 be Real;
assume c4 > 0 ;
then consider c5 being Nat such that
E6: for b1, b2 being Nat holds
not ( b1 >= c5 & b2 >= c5 & not dist (c3 . b1),(c3 . b2) < c4 ) by E3, E1;
take c6 = c5;
let c7, c8 be Nat;
assume ( c7 >= c6 & c8 >= c6 ) ;
then E7: dist (c3 . c7),(c3 . c8) < c4 by E6;
dist (c2 * (c3 . c7)),(c2 * (c3 . c8)) = dist H1(c1),(0 * (c3 . c8)) by E5, RLVECT_1:23
.= dist H1(c1),H1(c1) by RLVECT_1:23
.= 0 by BHSP_1:41 ;
then dist (c2 * (c3 . c7)),(c2 * (c3 . c8)) < c4 by E7, BHSP_1:44;
then dist ((c2 * c3) . c7),(c2 * (c3 . c8)) < c4 by NORMSP_1:def 8;
hence dist ((c2 * c3) . c7),((c2 * c3) . c8) < c4 by NORMSP_1:def 8;
end;
now
assume E5: c2 <> 0 ;
then E6: abs c2 > 0 by COMPLEX1:133;
let c4 be Real;
assume E7: c4 > 0 ;
E8: abs c2 <> 0 by E5, COMPLEX1:133;
0 / (abs c2) = 0 ;
then c4 / (abs c2) > 0 by E6, E7, REAL_1:73;
then consider c5 being Nat such that
E9: for b1, b2 being Nat holds
not ( b1 >= c5 & b2 >= c5 & not dist (c3 . b1),(c3 . b2) < c4 / (abs c2) ) by E3, E1;
take c6 = c5;
let c7, c8 be Nat;
assume ( c7 >= c6 & c8 >= c6 ) ;
then E10: dist (c3 . c7),(c3 . c8) < c4 / (abs c2) by E9;
E11: dist (c2 * (c3 . c7)),(c2 * (c3 . c8)) = ||.((c2 * (c3 . c7)) - (c2 * (c3 . c8))).|| by BHSP_1:def 5
.= ||.(c2 * ((c3 . c7) - (c3 . c8))).|| by RLVECT_1:48
.= (abs c2) * ||.((c3 . c7) - (c3 . c8)).|| by BHSP_1:33
.= (abs c2) * (dist (c3 . c7),(c3 . c8)) by BHSP_1:def 5 ;
(abs c2) * (c4 / (abs c2)) = (abs c2) * (((abs c2) " ) * c4) by XCMPLX_0:def 9
.= ((abs c2) * ((abs c2) " )) * c4
.= 1 * c4 by E8, XCMPLX_0:def 7
.= c4 ;
then dist (c2 * (c3 . c7)),(c2 * (c3 . c8)) < c4 by E6, E10, E11, XREAL_1:70;
then dist ((c2 * c3) . c7),(c2 * (c3 . c8)) < c4 by NORMSP_1:def 8;
hence dist ((c2 * c3) . c7),((c2 * c3) . c8) < c4 by NORMSP_1:def 8;
end;
hence c2 * c3 is_Cauchy_sequence by E4, E1;
end;

theorem :: BHSP_3:6
for b1 being RealUnitarySpace
for b2 being sequence of b1 holds
( b2 is_Cauchy_sequence implies - b2 is_Cauchy_sequence )
proof
let c1 be RealUnitarySpace;
let c2 be sequence of c1;
assume c2 is_Cauchy_sequence ;
then (- 1) * c2 is_Cauchy_sequence by E2;
hence - c2 is_Cauchy_sequence by BHSP_1:77;
end;

theorem E3: :: BHSP_3:7
for b1 being RealUnitarySpace
for b2 being Point of b1
for b3 being sequence of b1 holds
( b3 is_Cauchy_sequence implies b3 + b2 is_Cauchy_sequence )
proof
let c1 be RealUnitarySpace;
let c2 be Point of c1;
let c3 be sequence of c1;
assume E4: c3 is_Cauchy_sequence ;
let c4 be Real; :: according to BHSP_3:def 1
assume c4 > 0 ;
then consider c5 being Nat such that
E5: for b1, b2 being Nat holds
not ( b1 >= c5 & b2 >= c5 & not dist (c3 . b1),(c3 . b2) < c4 ) by E4, E1;
take c6 = c5;
let c7, c8 be Nat;
assume ( c7 >= c6 & c8 >= c6 ) ;
then E6: dist (c3 . c7),(c3 . c8) < c4 by E5;
dist ((c3 . c7) + c2),((c3 . c8) + c2) <= (dist (c3 . c7),(c3 . c8)) + (dist c2,c2) by BHSP_1:47;
then dist ((c3 . c7) + c2),((c3 . c8) + c2) <= (dist (c3 . c7),(c3 . c8)) + 0 by BHSP_1:41;
then dist ((c3 . c7) + c2),((c3 . c8) + c2) < c4 by E6, XXREAL_0:2;
then dist ((c3 + c2) . c7),((c3 . c8) + c2) < c4 by BHSP_1:def 12;
hence dist ((c3 + c2) . c7),((c3 + c2) . c8) < c4 by BHSP_1:def 12;
end;

theorem :: BHSP_3:8
for b1 being RealUnitarySpace
for b2 being Point of b1
for b3 being sequence of b1 holds
( b3 is_Cauchy_sequence implies b3 - b2 is_Cauchy_sequence )
proof
let c1 be RealUnitarySpace;
let c2 be Point of c1;
let c3 be sequence of c1;
assume c3 is_Cauchy_sequence ;
then c3 + (- c2) is_Cauchy_sequence by E3;
hence c3 - c2 is_Cauchy_sequence by BHSP_1:78;
end;

theorem :: BHSP_3:9
for b1 being RealUnitarySpace
for b2 being sequence of b1 holds
( b2 is convergent implies b2 is_Cauchy_sequence )
proof
let c1 be RealUnitarySpace;
let c2 be sequence of c1;
assume c2 is convergent ;
then consider c3 being Point of c1 such that
E4: for b1 being Real holds
not ( b1 > 0 & ( for b2 being Nat holds
ex b3 being Nat st
( b3 >= b2 & not dist (c2 . b3),c3 < b1 ) ) ) by BHSP_2:def 1;
let c4 be Real; :: according to BHSP_3:def 1
assume c4 > 0 ;
then c4 / 2 > 0 by SEQ_2:3;
then consider c5 being Nat such that
E5: for b1 being Nat holds
not ( b1 >= c5 & not dist (c2 . b1),c3 < c4 / 2 ) by E4;
take c6 = c5;
let c7, c8 be Nat;
assume E6: ( c7 >= c6 & c8 >= c6 ) ;
then E7: dist (c2 . c7),c3 < c4 / 2 by E5;
E8: dist (c2 . c8),c3 < c4 / 2 by E5, E6;
E9: dist (c2 . c7),(c2 . c8) <= (dist (c2 . c7),c3) + (dist c3,(c2 . c8)) by BHSP_1:42;
(dist (c2 . c7),c3) + (dist c3,(c2 . c8)) < (c4 / 2) + (c4 / 2) by E7, E8, XREAL_1:10;
hence dist (c2 . c7),(c2 . c8) < c4 by E9, XXREAL_0:2;
end;

definition
let c1 be RealUnitarySpace;
let c2, c3 be sequence of c1;
pred c2 is_compared_to c3 means :E4: :: BHSP_3:def 2
for b1 being Real holds
not ( b1 > 0 & ( for b2 being Nat holds
ex b3 being Nat st
( b3 >= b2 & not dist (a2 . b3),(a3 . b3) < b1 ) ) );
end;

:: deftheorem E4 defines is_compared_to BHSP_3:def 2 :
for b1 being RealUnitarySpace
for b2, b3 being sequence of b1 holds
( b2 is_compared_to b3 iff for b4 being Real holds
not ( b4 > 0 & ( for b5 being Nat holds
ex b6 being Nat st
( b6 >= b5 & not dist (b2 . b6),(b3 . b6) < b4 ) ) ) );

theorem E5: :: BHSP_3:10
for b1 being RealUnitarySpace
for b2 being sequence of b1 holds b2 is_compared_to b2
proof
let c1 be RealUnitarySpace;
let c2 be sequence of c1;
let c3 be Real; :: according to BHSP_3:def 2
assume E6: c3 > 0 ;
take c4 = 0;
let c5 be Nat;
assume c5 >= c4 ;
thus dist (c2 . c5),(c2 . c5) < c3 by E6, BHSP_1:41;
end;

theorem E6: :: BHSP_3:11
for b1 being RealUnitarySpace
for b2, b3 being sequence of b1 holds
( b2 is_compared_to b3 implies b3 is_compared_to b2 )
proof
let c1 be RealUnitarySpace;
let c2, c3 be sequence of c1;
assume E7: c2 is_compared_to c3 ;
let c4 be Real; :: according to BHSP_3:def 2
assume c4 > 0 ;
then consider c5 being Nat such that
E8: for b1 being Nat holds
not ( b1 >= c5 & not dist (c2 . b1),(c3 . b1) < c4 ) by E7, E4;
take c6 = c5;
let c7 be Nat;
assume c7 >= c6 ;
hence dist (c3 . c7),(c2 . c7) < c4 by E8;
end;

definition
let c1 be RealUnitarySpace;
let c2, c3 be sequence of c1;
redefine pred is_compared_to as c2 is_compared_to c3;
reflexivity
for b1 being sequence of c1 holds b1 is_compared_to b1
by E5;
symmetry
for b1, b2 being sequence of c1 holds
( b1 is_compared_to b2 implies b2 is_compared_to b1 )
by E6;
end;

theorem :: BHSP_3:12
for b1 being RealUnitarySpace
for b2, b3, b4 being sequence of b1 holds
( ( b2 is_compared_to b3 & b3 is_compared_to b4 ) implies ( b2 is_compared_to b4 ) )
proof
let c1 be RealUnitarySpace;
let c2, c3, c4 be sequence of c1;
assume that
E7: c2 is_compared_to c3 and
E8: c3 is_compared_to c4 ;
let c5 be Real; :: according to BHSP_3:def 2
assume c5 > 0 ;
then E9: c5 / 2 > 0 by SEQ_2:3;
then consider c6 being Nat such that
E10: for b1 being Nat holds
not ( b1 >= c6 & not dist (c2 . b1),(c3 . b1) < c5 / 2 ) by E7, E4;
consider c7 being Nat such that
E11: for b1 being Nat holds
not ( b1 >= c7 & not dist (c3 . b1),(c4 . b1) < c5 / 2 ) by E8, E9, E4;
take c8 = c6 + c7;
let c9 be Nat;
assume E12: c9 >= c8 ;
c6 + c7 >= c6 by NAT_1:37;
then c9 >= c6 by E12, XXREAL_0:2;
then E13: dist (c2 . c9),(c3 . c9) < c5 / 2 by E10;
c8 >= c7 by NAT_1:37;
then c9 >= c7 by E12, XXREAL_0:2;
then dist (c3 . c9),(c4 . c9) < c5 / 2 by E11;
then E14: (dist (c2 . c9),(c3 . c9)) + (dist (c3 . c9),(c4 . c9)) < (c5 / 2) + (c5 / 2) by E13, XREAL_1:10;
dist (c2 . c9),(c4 . c9) <= (dist (c2 . c9),(c3 . c9)) + (dist (c3 . c9),(c4 . c9)) by BHSP_1:42;
hence dist (c2 . c9),(c4 . c9) < c5 by E14, XXREAL_0:2;
end;

theorem :: BHSP_3:13
for b1 being RealUnitarySpace
for b2, b3 being sequence of b1 holds
( b2 is_compared_to b3 iff for b4 being Real holds
not ( b4 > 0 & ( for b5 being Nat holds
ex b6 being Nat st
( b6 >= b5 & not ||.((b2 . b6) - (b3 . b6)).|| < b4 ) ) ) )
proof
let c1 be RealUnitarySpace;
let c2, c3 be sequence of c1;
thus ( c2 is_compared_to c3 implies for b1 being Real holds
not ( b1 > 0 & ( for b2 being Nat holds
ex b3 being Nat st
( b3 >= b2 & not ||.((c2 . b3) - (c3 . b3)).|| < b1 ) ) ) )
proof
assume E7: c2 is_compared_to c3 ;
let c4 be Real;
assume c4 > 0 ;
then consider c5 being Nat such that
E8: for b1 being Nat holds
not ( b1 >= c5 & not dist (c2 . b1),(c3 . b1) < c4 ) by E7, E4;
take c6 = c5;
let c7 be Nat;
assume c7 >= c6 ;
then dist (c2 . c7),(c3 . c7) < c4 by E8;
hence ||.((c2 . c7) - (c3 . c7)).|| < c4 by BHSP_1:def 5;
end;
( ( for b1 being Real holds
not ( b1 > 0 & ( for b2 being Nat holds
ex b3 being Nat st
( b3 >= b2 & not ||.((c2 . b3) - (c3 . b3)).|| < b1 ) ) ) ) implies c2 is_compared_to c3 )
proof
assume E7: for b1 being Real holds
not ( b1 > 0 & ( for b2 being Nat holds
ex b3 being Nat st
( b3 >= b2 & not ||.((c2 . b3) - (c3 . b3)).|| < b1 ) ) ) ;
let c4 be Real; :: according to BHSP_3:def 2
assume c4 > 0 ;
then consider c5 being Nat such that
E8: for b1 being Nat holds
not ( b1 >= c5 & not ||.((c2 . b1) - (c3 . b1)).|| < c4 ) by E7;
take c6 = c5;
let c7 be Nat;
assume c7 >= c6 ;
then ||.((c2 . c7) - (c3 . c7)).|| < c4 by E8;
hence dist (c2 . c7),(c3 . c7) < c4 by BHSP_1:def 5;
end;
hence ( ( for b1 being Real holds
not ( b1 > 0 & ( for b2 being Nat holds
ex b3 being Nat st
( b3 >= b2 & not ||.((c2 . b3) - (c3 . b3)).|| < b1 ) ) ) ) implies c2 is_compared_to c3 ) ;
end;

theorem :: BHSP_3:14
for b1 being RealUnitarySpace
for b2, b3 being sequence of b1 holds
( ex b4 being Nat st
for b5 being Nat holds
( b5 >= b4 implies b2 . b5 = b3 . b5 ) implies b2 is_compared_to b3 )
proof
let c1 be RealUnitarySpace;
let c2, c3 be sequence of c1;
assume E7: ex b1 being Nat st
for b2 being Nat holds
( b2 >= b1 implies c2 . b2 = c3 . b2 ) ;
let c4 be Real; :: according to BHSP_3:def 2
assume E8: c4 > 0 ;
consider c5 being Nat such that
E9: for b1 being Nat holds
( b1 >= c5 implies c2 . b1 = c3 . b1 ) by E7;
take c6 = c5;
let c7 be Nat;
assume c7 >= c6 ;
then dist (c2 . c7),(c3 . c7) = dist (c2 . c7),(c2 . c7) by E9
.= 0 by BHSP_1:41 ;
hence dist (c2 . c7),(c3 . c7) < c4 by E8;
end;

theorem :: BHSP_3:15
for b1 being RealUnitarySpace
for b2, b3 being sequence of b1 holds
( ( b2 is_Cauchy_sequence & b2 is_compared_to b3 ) implies ( b3 is_Cauchy_sequence ) )
proof
let c1 be RealUnitarySpace;
let c2, c3 be sequence of c1;
assume that
E7: c2 is_Cauchy_sequence and
E8: c2 is_compared_to c3 ;
let c4 be Real; :: according to BHSP_3:def 1
assume c4 > 0 ;
then E9: c4 / 3 > 0 by XREAL_1:224;
then consider c5 being Nat such that
E10: for b1, b2 being Nat holds
not ( b1 >= c5 & b2 >= c5 & not dist (c2 . b1),(c2 . b2) < c4 / 3 ) by E7, E1;
consider c6 being Nat such that
E11: for b1 being Nat holds
not ( b1 >= c6 & not dist (c2 . b1),(c3 . b1) < c4 / 3 ) by E8, E9, E4;
take c7 = c5 + c6;
let c8, c9 be Nat;
assume E12: ( c8 >= c7 & c9 >= c7 ) ;
c5 + c6 >= c5 by NAT_1:37;
then ( c8 >= c5 & c9 >= c5 ) by E12, XXREAL_0:2;
then E13: dist (c2 . c8),(c2 . c9) < c4 / 3 by E10;
E14: c7 >= c6 by NAT_1:37;
then c8 >= c6 by E12, XXREAL_0:2;
then E15: dist (c2 . c8),(c3 . c8) < c4 / 3 by E11;
c9 >= c6 by E12, E14, XXREAL_0:2;
then E16: dist (c2 . c9),(c3 . c9) < c4 / 3 by E11;
E17: (dist (c3 . c8),(c2 . c8)) + (dist (c2 . c8),(c2 . c9)) < (c4 / 3) + (c4 / 3) by E13, E15, XREAL_1:10;
dist (c3 . c8),(c2 . c9) <= (dist (c3 . c8),(c2 . c8)) + (dist (c2 . c8),(c2 . c9)) by BHSP_1:42;
then dist (c3 . c8),(c2 . c9) < (c4 / 3) + (c4 / 3) by E17, XXREAL_0:2;
then E18: (dist (c3 . c8),(c2 . c9)) + (dist (c2 . c9),(c3 . c9)) < ((c4 / 3) + (c4 / 3)) + (c4 / 3) by E16, XREAL_1:10;
dist (c3 . c8),(c3 . c9) <= (dist (c3 . c8),(c2 . c9)) + (dist (c2 . c9),(c3 . c9)) by BHSP_1:42;
hence dist (c3 . c8),(c3 . c9) < c4 by E18, XXREAL_0:2;
end;

theorem :: BHSP_3:16
for b1 being RealUnitarySpace
for b2, b3 being sequence of b1 holds
( ( b2 is convergent & b2 is_compared_to b3 ) implies ( b3 is convergent ) )
proof
let c1 be RealUnitarySpace;
let c2, c3 be sequence of c1;
assume that
E7: c2 is convergent and
E8: c2 is_compared_to c3 ;
now
let c4 be Real;
assume c4 > 0 ;
then E9: c4 / 2 > 0 by SEQ_2:3;
then consider c5 being Nat such that
E10: for b1 being Nat holds
not ( b1 >= c5 & not dist (c2 . b1),(lim c2) < c4 / 2 ) by E7, BHSP_2:def 2;
consider c6 being Nat such that
E11: for b1 being Nat holds
not ( b1 >= c6 & not dist (c2 . b1),(c3 . b1) < c4 / 2 ) by E8, E9, E4;
take c7 = c5 + c6;
let c8 be Nat;
assume E12: c8 >= c7 ;
c5 + c6 >= c5 by NAT_1:37;
then c8 >= c5 by E12, XXREAL_0:2;
then E13: dist (c2 . c8),(lim c2) < c4 / 2 by E10;
c7 >= c6 by NAT_1:37;
then c8 >= c6 by E12, XXREAL_0:2;
then dist (c2 . c8),(c3 . c8) < c4 / 2 by E11;
then E14: (dist (c3 . c8),(c2 . c8)) + (dist (c2 . c8),(lim c2)) < (c4 / 2) + (c4 / 2) by E13, XREAL_1:10;
dist (c3 . c8),(lim c2) <= (dist (c3 . c8),(c2 . c8)) + (dist (c2 . c8),(lim c2)) by BHSP_1:42;
hence dist (c3 . c8),(lim c2) < c4 by E14, XXREAL_0:2;
end;
hence c3 is convergent by BHSP_2:def 1;
end;

theorem :: BHSP_3:17
for b1 being RealUnitarySpace
for b2 being Point of b1
for b3, b4 being sequence of b1 holds
( ( b3 is convergent & lim b3 = b2 & b3 is_compared_to b4 ) implies ( ( b4 is convergent & lim b4 = b2 ) ) )
proof
let c1 be RealUnitarySpace;
let c2 be Point of c1;
let c3, c4 be sequence of c1;
assume that
E7: c3 is convergent and
E8: lim c3 = c2 and
E9: c3 is_compared_to c4 ;
E10: now
let c5 be Real;
assume c5 > 0 ;
then E11: c5 / 2 > 0 by SEQ_2:3;
then consider c6 being Nat such that
E12: for b1 being Nat holds
not ( b1 >= c6 & not dist (c3 . b1),c2 < c5 / 2 ) by E7, E8, BHSP_2:def 2;
consider c7 being Nat such that
E13: for b1 being Nat holds
not ( b1 >= c7 & not dist (c3 . b1),(c4 . b1) < c5 / 2 ) by E9, E11, E4;
take c8 = c6 + c7;
let c9 be Nat;
assume E14: c9 >= c8 ;
c6 + c7 >= c6 by NAT_1:37;
then c9 >= c6 by E14, XXREAL_0:2;
then E15: dist (c3 . c9),c2 < c5 / 2 by E12;
c8 >= c7 by NAT_1:37;
then c9 >= c7 by E14, XXREAL_0:2;
then dist (c3 . c9),(c4 . c9) < c5 / 2 by E13;
then E16: (dist (c4 . c9),(c3 . c9)) + (dist (c3 . c9),c2) < (c5 / 2) + (c5 / 2) by E15, XREAL_1:10;
dist (c4 . c9),c2 <= (dist (c4 . c9),(c3 . c9)) + (dist (c3 . c9),c2) by BHSP_1:42;
hence dist (c4 . c9),c2 < c5 by E16, XXREAL_0:2;
end;
then c4 is convergent by BHSP_2:def 1;
hence ( c4 is convergent & lim c4 = c2 ) by E10, BHSP_2:def 2;
end;

definition
let c1 be RealUnitarySpace;
let c2 be sequence of c1;
attr a2 is bounded means :E7: :: BHSP_3:def 3
ex b1 being Real st
( b1 > 0 & ( for b2 being Nat holds ||.(a2 . b2).|| <= b1 ) );
end;

:: deftheorem E7 defines bounded BHSP_3:def 3 :
for b1 being RealUnitarySpace
for b2 being sequence of b1 holds
( b2 is bounded iff ex b3 being Real st
( b3 > 0 & ( for b4 being Nat holds ||.(b2 . b4).|| <= b3 ) ) );

theorem E8: :: BHSP_3:18
for b1 being RealUnitarySpace
for b2, b3 being sequence of b1 holds
( ( b2 is bounded & b3 is bounded ) implies ( b2 + b3 is bounded ) )
proof
let c1 be RealUnitarySpace;
let c2, c3 be sequence of c1;
assume that
E9: c2 is bounded and
E10: c3 is bounded ;
consider c4 being Real such that
E11: c4 > 0 and
E12: for b1 being Nat holds ||.(c2 . b1).|| <= c4 by E9, E7;
consider c5 being Real such that
E13: c5 > 0 and
E14: for b1 being Nat holds ||.(c3 . b1).|| <= c5 by E10, E7;
E15: c4 + c5 > 0 + 0 by E11, E13, XREAL_1:10;
now
let c6 be Nat;
E16: ||.(c2 . c6).|| <= c4 by E12;
||.(c3 . c6).|| <= c5 by E14;
then E17: ||.(c2 . c6).|| + ||.(c3 . c6).|| <= c4 + c5 by E16, XREAL_1:9;
||.((c2 + c3) . c6).|| = ||.((c2 . c6) + (c3