International Journal of Scientific and Innovative Mathematical Research (IJSIMR)
Volume 2, Issue 6, June 2014, PP 603-610
ISSN 2347-307X (Print) & ISSN 2347-3142 (Online)
www.arcjournals.org
©ARC Page | 603
About the Strictly Convex and Uniformly Convex Normed and
2-Normed Spaces
Risto Malčeski
Faculty for informatics
FON University, Skopje, Macedonia
risto.malceski@gmail.com
Ljupcho Nastovski
Faculty of Natural science
Sts.”Cyril and Methodius”, Skopje, Macedonia
ljupcona@pmf.ukim.mk
Biljana Načevska
Faculty of Electrical Engineering and
Information
Sts.”Cyril and Methodius”, Skopje, Macedonia
biljanan@feit.ukim.edu.mk
Admir Huseini
Independent researcher, RISAT
Skopje, Macedonia
huseini@risat.org
Abstract: In [1] A. Khan introduces the notion of uniformly convex 2-normed space and prove some
properties of the uniformly convex 2-normed spaces. In this work, further properties of the uniformly
convex 2-normed spaces are given and the question of the convexity of a normed space in which the norm is
induced by 2-norm is analysed.
Keywords: 2-normed space, 2-pre-Hibert space, convergent sequence, strictly convex space, uniformly
convex space
2010 Mathematics Subject Classification. 46B20, 46C05
1. INTRODUCTION
The concept of a uniformly convex 2-normed space is introduced by A. Khan. For our further
investigation, we will introduce the definition of the uniformly convex 2-normed space in its
equivalent form, as follows.
Definition 1 ([1]). A 2-normed space ( ,|| , ||) L is uniformly convex if for every 0 there exists
() 0 such that || , || || , || 1 xz yz , || , || x yz and (, ) z Vxy implies
|| , || 2(1 ( )) x yz ,
where (, ) Vxy is the subspace generated by the vectors x and y .
Example 1 ([1]). A 2-pre-Hibert space is a 2-normed space in which the norm is introduced by
2
|| , || (, | ) xy xxy and the parallelepiped law is satisfied
2 2 2 2
|| , || || , || 2(|| , || || , || ) x yz x yz xz yz . (1)
If 0 is given and || , || || , || 1 xz yz , || , || x yz and (, ) z Vxy , then from the equality (1)
it follows that for
2
2
() 1 1 () 0 the following
2 1/2 2 1/2
|| , || (4 || , || ) (4 ) 2(1 ( )) x yz x yz
holds. It means, that ( ,(, | )) L is uniformly convex space.
Let z be a fixed nonzero element in L , () Vz be the subspace of L generated by z and let
z
L be
the quotient space / () LVz . For x L by
z
x we denote the class of equivalence of x over () Vz .
Clearly,
z
L is a linear space with the operations of adding the two vectors and multiplying a