Vitali Theorems in Non-Newtonian Sense and Non-Newtonian
Measurable Functions
OGUZ OGUR, ZEKIYE GUNES
Department of Mathematics,
Giresun University,
Giresun-Gure,
TURKEY
Abstract: In this paper, we first state the νVitali theorems in the non-Newtonian sense. In the second part, we
give the definition of the non-Newtonian measurable function and the relation between νmeasurable and real
measurable functions. We also study some basic properties of ν-measurable functions.
Key-Words: Non-Newtonian measurable set, non-Newtonian Vitali set, non-Newtonian measurable function
Received: March 23, 2024. Revised: August 25, 2024. Accepted: September 18, 2024. Published: October 16, 2024.
1 Introduction
Non-Newtonian calculus, which has found
applications in various fields such as engineering,
mathematics, finance, economics, medicine, and
biomedical sciences, was developed between
1967 and 1970 as an alternative to the classical
calculus of Newton and Leibniz, [1], [2]. The
foundational book titled Non-Newtonian Calculus,
which laid the groundwork for this alternative
calculus, was published in 1972 by [3]. The
concepts of derivative and integral in the context of
metacalculus were explored by [4], while geometric
calculus and its applications were examined in
[5]. The non-Newtonian Lebesgue measure for
non-Newtonian open sets was defined and studied
in[6]. Finally, the non-Newtonian measure for
closed non-Newtonian sets, along with some related
theorems, was defined and studied in [7]. For more
details see, [8], [9], [10], [11], [12], [13], [14], [15],
[16], [17], [18], [19], [20], [21], [22].
Let νbe a generator, which means νis a
one-to-one function whose domain is real numbers
and whose range is a subset Aof R. Let ˙p, ˙qA.
Then, νarithmetics are defined as follows;
νaddition ˙p˙
+ ˙q=ν{ν1( ˙p) + ν1( ˙q)}
νsubtraction ˙p˙
˙q=ν{ν1( ˙p)ν1( ˙q)}
νmultiplicative ˙p˙
×˙q=ν{ν1( ˙p)×ν1( ˙q)}
νdivision
(ν1( ˙q)= 0) ˙p˙
/ ˙q=ν{ν1( ˙p)/ν1( ˙q)}
νorder ˙p˙
˙qν1( ˙p)ν1( ˙q)
Numbers with x˙
>˙
0are called νpositive numbers,
and numbers with x˙
<˙
0are called νnegative
numbers. The set of νintegers is
Zν=Z(N) = . . . , ν(2), ν(1), ν(0), ν(1), ν(2), . . . .
The set Rν=R(N) = {ν(a) : aR}is called
the set of non-Newtonian real numbers.
The absolute non-Newtonian value of ˙aAin
the subset ARνis denoted by |˙a|Nand define as
follows;
|˙a|ν=
˙a , ˙a˙
(0)
ν(0) ,˙a=ν(0)
ν(0) ˙
˙a , ˙a˙
(0)
Accordingly,
˙a2N
N=|˙a|N=ν|ν1( ˙a)|
is written for each ˙uin the set ARν[3], [8].
Definition 1. The non-Newtonian outer measure of
a nonempty νbounded set Kis the largest lower
bound of the measures of all νbounded, νopen
sets containing the set K. So it is defined by
m
NK=νinf
KG{mNG}
[7].
Definition 2. The non-Newtonian interior measure of
a nonempty νbounded set Kis the smallest upper
bound of the measures of all νclosed sets contained
in the set K. So it is defined by
mNK=νsup
FK{mNF}
[7].
Theorem 1. Let be given a νbounded set K. If is
aνopen set containing the set K, then we have the
following equation;
m
NK˙
+mNCK
=mN
[7].
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Definition 3. If the non-Newtonian interior and
exterior measure of a νbounded set Kare equal,
the set Kis called a non-Newtonian Lebesgue
measurable set, or simply the νmeasurable set, [7].
Theorem 2. If the set Kis the νmeasurable set in
Rν, then ν1(K)is the measurable set in R, [7].
Theorem 3. Let be given a νbounded set E.
If the set E can be written as a combination of
finite or countably infinite sets of pairwise disjoint
νmeasurable Eksets, then Eis νmeasurable and
mNE=ν
k
mNEk
equality is satisfied, [23].
2 Main Results
2.1 Vitali Theorems
Definition 4. Let Kbe a set of νpoints and Ba
family of νclosed intervals, none of which are single
points.If for every xKpoint and for every ˙ϵ˙
>˙
0
there is a νclosed bBinterval such that
xb, mNb˙
<˙ϵ,
then, the set Kis said to be contained by the family
Bin the νVitali sense.
In other words, if every point of the set Klies in
arbitrarily small νclosed intervals belonging to the
family B, then the set Kis covered by the family B
in the νVitali sense.
If the set Kis contained by the Bin the νVitali
sense, then the set ν1(K)is also contained by a
family in the Vitali sense. Let Bis the family of
νclosed sets bwhich do not consist of a single point
and let B1be the family of ν1(b)closed sets that do
not consist of a single point. Then, for xKand
for each ˙ϵ˙
>˙
0, there is an νclosed interval bB
such that
xb, mNb˙
<˙ϵ.
Then, we have
ν1(x)ν1(b)
and ν1(b)B1since bBso we get
ν1(mN(b)) < ν1( ˙ϵ)
ν1ν{m(ν1(b))}< ϵ
m(ν1(b)) < ϵ (ϵ > 0)
ν1(K)Vitali
Theorem 4. If a νbounded set Kis covered by a
family of closed intervals Bin the νVitali sense,
then it is possible to find a finite or countable family
of νclosed intervals bkin the set Bsuch that
bkbi=(k=i)m
NK\
k
bk=˙
0.
Proof. Since the set Kis νbounded, the set ν1(K)
is bounded and is covered by the family B1which
consist of closed intervals. By the Vitali’s theorem it
is possible to find a finite or countable closed interval
family ν1(bk)in the set B1, such that
ν1(bk)ν1(bi) = (k=i)
mν1(K)\
k
ν1(bk)= 0
ν{ν1(bkbi)}=ν{∅}(k=i)
mν1(K)\ν1
k
bk= 0
bkbi=(k=i)
νmν1K\
k
bk=ν(0)
bkbi=(k=i)
m
NK\
k
bk=˙
0
which gives the proof.
Theorem 5. Under the hypotheses of Theorem 4,
for every ˙ϵ˙
>˙
0there is a finite system b1, b2, . . . , bn
consisting of pairwise disjoint νclosed intervals of
the system Bsuch that
m
NK\
n
k
bk˙
<˙ϵ.
Proof. If the set Kis covered by a family of closed
intervals Bin the sense of νVitali, then the set
ν1(K)is also covered by a family of closed intervals
B1in the sense of Vitali. The B1system has a finite
ν1(b1), ν1(b2), . . . , ν1(bn)
system of pairwise disjoint closed intervals. Thus we
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get
mν1(K)\
n
k
ν1(bk)< ϵ
mν1(K)\ν1n
k
bk< ϵ
νmν1K\
n
k
bk< ν(ϵ)
m
NK\
n
k
bk<˙ϵ
ν1m
NK\
n
k
bk< ν1( ˙ϵ)
m
NK\
n
k
bk˙
<˙ϵ
.
2.2 Measurable Functions
Definition 5. Let
fν:XRνRν
˙afν( ˙a).
If for ˙
βRν, the set
A={˙aX:fν( ˙a)˙
>˙
β}
is νmeasurable, that is,
m
NA=mNA
then, the function fνis called a non-Newtonian
measurable function, or simply a νmeasurable
function.
Theorem 6. Let fν:XRνRνbe a function.
The following expressions are equivalent; for ˙
β
Rν
a) the set A˙
β={˙aX:fν( ˙a)˙
>˙
β}is the
νmeasurable set,
b) the set B˙
β={˙aX:fν( ˙a)˙
˙
β}is the
νmeasurable set,
c) the set C˙
β={˙aX:fν( ˙a)˙
˙
β}is the
νmeasurable set,
b) the set D˙
β={˙aX:fν( ˙a)˙
<˙
β}is the
νmeasurable set.
Proof. It is obvious that A˙
β=X\B˙
β,B˙
β=X\A˙
β.
(a)(b):Since A˙
βis νmeasurable, its
complement, B˙
β, is also νmeasurable.
(b)(a): Since B˙
βis νmeasurable, its
complement, A˙
β, is also νmeasurable.
Thus, we get (a)(b).
Since C˙
β=X\D˙
βis D˙
β=X\C˙
β(c)(d).
(a)(c): For ˙
βRν, let A˙
β={˙aX:
fν( ˙a)˙
>˙
β}be the νmeasurable set.
For every ˙m νpositive integer, we have ˙
β˙
˙
1
mRν
since ˙
βRνand ˙
1
mRνand so A˙
β˙
˙
1
m
is a
νmeasurable set.
Thus
A˙
β˙
˙
1
m
={˙aX:fν( ˙a)˙
>˙
β˙
˙
1
m}
and we get
m=1
A˙
β˙
˙
1
m
=
m=1 ˙aX:fν( ˙a)˙
>˙
β˙
˙
1
m
={˙aX:fν( ˙a)˙
˙
β}=C˙
β
is the νmeasurable set.
(c)(a): For ˙
βRν,C˙
β={˙aX:fν( ˙a)˙
˙
β}
be a νmeasurable set.
For every ˙m νpositive integer, we have ˙
β˙
+˙
1
mRν
since ˙
βRνand ˙
1
mRνand so C˙
β˙
+˙
1
m
is the
νmeasurable set.
Again
C˙
β˙
+˙
1
m
={˙aX:fν( ˙a)˙
˙
β˙
+˙
1
m}
and we get
n=1
C˙
β˙
+˙
1
m
=
m=1 ˙aX:fν( ˙a)˙
˙
β˙
+˙
1
m
={˙aX:fν( ˙a)˙
>˙
β}=A˙
β
is the νmeasurable set which gives (a)(c).
Theorem 7. If
fν:XRνRν
˙afν( ˙a)
is a non-Newtonian measurable function, then
ν1fνν:ν1(X)RR
a(ν1fνν)(a)
is a measurable function.
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Proof. Since fνis a non-Newtonian measurable
function, we have
˙
βRν,{˙aX:fν( ˙a)˙
>˙
β}is the νmeasurable
set. For βR, the set
ν1({˙aX:fν( ˙a)˙
>˙
β})
{ν1( ˙a)ν1(X) : fν( ˙a)˙
>˙
β}
{aν1(X) : ν1(fν(ν(a))) > ν1(˙
β)}
{aν1(X) : (ν1fνν)(a)> β}
is measurable. This completes the proof.
Example 1. The non-Newtonian constant function
fν:XRνRν
˙afν( ˙a) = ˙c, ˙cRν
is a νmeasurable.
Proof. For ˙
βRν, it can be shown that the set
{˙aX:fν( ˙a) = ˙c˙
>˙
β}
is νmeasurable.
(i) Let ˙
β˙
˙c. Then, the set
fν( ˙a)˙
>˙
β˙
˙c
{˙aX:fν( ˙a)˙
>˙
β}=
is νmeasurable.
(ii) Let ˙
β˙
<˙c. Thus, the set
{˙aX:fν( ˙a)˙
>˙
β}=X
is νmeasurable.
Then the non-Newtonian constant function is
νmeasurable.
Example 2. For ˙aRν, the set {˙aX:fν(˙a) =
˙
β}is a-measurable if
fν:XRνRν
˙afν( ˙a)
is a non-Newtonian measurable function.
Proof. It is easy to see the following equality:
{˙aX:fν( ˙a) = ˙
β}
={˙aX:fν( ˙a)˙
˙
β}∩{˙aX:fν( ˙a)˙
˙
β}.
Since finite number of intersections of νmeasurable
sets are νmeasurable the proof is completed.
Definition 6. Given a set E, the νcharacteristic
function of Eis denoted by νχand defined by
νχE=˙
1, x E
˙
0, x /E
Example 3. If Eis νmeasurable set, the the
function νχEis a νmeasurable function.
Proof. For βRνwe show that the set
xX:νχE(X)˙
>˙
βis a νmeasurable.
i) If ˙
β˙
<˙
0, then the set
xX:νχE(X)˙
>˙
β=X
is νmeasurable.
ii) Let ˙
0˙
˙
β˙
<˙
1. Then the set
xX:νχE(X)˙
>˙
β=E
is νmeasurable.
iii) Let ˙
β˙
˙
1.
xX:νχE(X)˙
>˙
β=
set is νmeasurable.
Hence, the function νχEis νmeasurable function
when the set Eis νmeasurable.
Theorem 8. If the function fνis νmeasurable
non-Newtonian real-valued function and ˙cRν, then
the function ˙c˙
×fνis νmeasurable.
Proof. To show that the function ( ˙c˙
×fν)( ˙a) =
˙c˙
×fν( ˙a)is νmeasurable, the set
{˙aX: ( ˙c˙
×fν)( ˙a)˙
>˙
β}
must be shown to be νmeasurable.
i) If ˙c=˙
0, the set
{˙aX: ( ˙c˙
×fν)( ˙a)˙
>˙
β}=Xif ˙
β˙
<˙
0
is νmeasurable and the set
{˙aX: ( ˙c˙
×fν)( ˙a)˙
>˙
β}=if ˙
β˙
˙
0
is νmeasurable.
which shows that the ˙c˙
×fνfunction is νmeasurable.
ii) Let ˙c˙
>˙
0. We write
{˙aX: ˙c˙
×fν( ˙a)˙
>˙
β}={˙aX:fν( ˙a)˙
>˙
β˙
/ ˙c}.
Since ˙
β˙
/ ˙cRνand the fνfunction is νmeasurable,
the set {˙aX: ˙c˙
×fν( ˙a)˙
>˙
β}is νmeasurable.
iii) Let ˙c˙
<˙
0. The set
{˙aX: ˙c˙
×fν( ˙a)˙
<˙
β}={˙aX:fν( ˙a)˙
<˙
β˙
/ ˙c}
is νmeasurable since ˙
β˙
/ ˙cRνand the function fν
is νmeasurable.
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Theorem 9. If the function fνis νmeasurable,
then the non-Newtonian real-valued function f2N
νis
νmeasurable.
Proof.
i) If ˙
β˙
<˙
0then {˙aX: [fν( ˙a)]2N˙
>˙
β}=Xset is
νmeasurable.
ii) If ˙
β˙
˙
0then we have
{˙aX: [fν( ˙a)]2N˙
>˙
β}
={˙aX:|fν( ˙a)|N˙
>˙
β
N
}
={˙aX:fν( ˙a)˙
>˙
β
N
}∪{˙aX:fν( ˙a)˙
<˙
˙
β
N
}
which shows the function f2N
νis νmeasurable.
Theorem 10. If non-Newtonian real-valued functions
fν, gνare νmeasurable, then the function fν˙
+gνis
νmeasurable.
Proof. Since the functions fν, gνare νmeasurable,
then we have ν1fνν, ν1gννare real-valued
measurable functions. Therefore, we get (ν1fν
ν)+(ν1gνν)is measurable.
Thus, since
(ν1fνν)(a)+(ν1gνν)(a)
=ν1(ν{(ν1fνν)(a)+(ν1gνν)(a)})
=ν1(ν{ν1(fν(ν(a))) + ν1(gν(ν(a)))})
=ν1(fν(ν(a)) ˙
+gν(ν(a)))
=ν1((fν˙
+gν)(ν(a)))
= (ν1(fν˙
+gν)ν)(a)
is a measurable function for aν1(X), then the
function fν˙
+gνis νmeasurable.
Theorem 11. If fν, gνare νmeasurable, then the
function fν˙
×gνis νmeasurable.
Proof. If fνand gνare νmeasurable, then ν1fν
ν, ν1gννare real-valued measurable functions.
Therefore, the (ν1fνν)×(ν1gνν)function
is measurable. Thus, since
(ν1fνν)(a)×(ν1gνν)(a)
=ν1(ν{(ν1fνν(a)) ×(ν1gνν(a))})
=ν1(ν{ν1(fν(ν(a))) ×ν1(gν(ν(a)))})
=ν1(fν(ν(a)) ˙
×gν(ν(a)))
=ν1((fν˙
×gν)(ν(a)))
= (ν1(fν˙
×gν)ν)(a)
is a measurable function for aν1(X), then the
function fν˙
×gνis νmeasurable.
Theorem 12. If the function fνis νmeasurable,
then the function |fν|Nis νmeasurable.
Proof.
i) If ˙
β˙
<˙
0, the set {˙aX:|fν( ˙a)|N˙
>˙
β}=Xis
νmeasurable.
ii) Let ˙
β˙
˙
0. Then the set {˙aX:|fν( ˙a)|N˙
>˙
β}is
νmeasurable since
{˙aX:|fν( ˙a)|N˙
>˙
β}
={˙aX:fν( ˙a)˙
>˙
β}∪{˙aX:fν( ˙a)˙
<˙
˙
β}
is νmeasurable. This shows that the function |fν|N
is νmeasurable.
3 Conclusion
In this study, we first give the νVitali theorems
in the non-Newtonian sense. In the second
part, we give the definition of the non-Newtonian
measurable function. Also, we show that a function
νmeasurable if and only if the function ν1fννis
a measurable function.This can be seen as the crucial
step in the definition of the Lebesgue integral in
the non-Newtonian sense. We also investigate some
basic properties of νmeasurable functions.
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Volume 23, 2024
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Contribution of Individual Authors to the
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WSEAS TRANSACTIONS on MATHEMATICS
DOI: 10.37394/23206.2024.23.66
Oguz Ogur, Zekiye Gunes
E-ISSN: 2224-2880
632
Volume 23, 2024