11.fixed point theorem of discontinuity and weak compatibility in non complete non archimedean menger pm-spaces

Network and Complex Systems www.iiste.org
ISSN 2224-610X (Paper) ISSN 2225-0603 (Online)
Vol 1, No.1, 2011

Fixed Point Theorem Of Discontinuity And Weak
Compatibility In Non complete Non-Archimedean Menger
PM-Spaces
Pooja Sharma (Corresponding author)
Career College, Barkatullah University
M.I.G-9 sector 4B Saket Nager Bhopal, India
Tel: +919301030702 E-mail: poojasharma020283@gmail.com

R.S.Chandel
Govt. Geetanjali College, Barkatullah University
Tulsi Nager, Bhopal, India
Tel: +919425650235 E-mail: rschandel_2009@yahoo.com
Abstract
The aim of this paper is to prove a related common fixed point theorem for six weakly compatible self
maps in non complete non-Archimedean menger PM-spaces, without using the condition of continuity and
give a set of alternative conditions in place of completeness of the space.
Keywords: key words, Non-Archimedean Menger PM-space, R-weakly commutting maps, fixed points.
1. Introduction
There have been a number of generalizations of metric spaces, one of them is designated as Menger space
propounded by Menger in 1972. In 1976, Jungck established common fixed point theorems for commuting
maps generalizing the Banach’s fixed point theorem. Sessa (1982) defined a generalization of commutativity
called weak commutativity. Futher Jungck (1986) introduced more generalized commutativity, which is
called compatibility. In 1998, Jungck & Rhodes introduced the notion of weakly compatible maps and
showed that compatible maps are weakly compatible but converse need not true. Sharma & Deshpande
(2006) improved the results of Sharma & Singh (1982), Cho (1997), Sharma & Deshpande (2006). Chugh
and Kumar (2001) proved some interesting results in metric spaces for weakly compatible maps without
appeal to continuity. Sharma and deshpande (2006) proved some results in non complete Menger spaces, for
weakly compatible maps without appeal to continuity. In this Paper, we prove a common fixed point theorem
for six maps has been proved using the concept of weak compatibility without using condition of continuity.
We will improve results of Sharma & Deshpande (2006) and many others.
Preliminary notes
Definition 1.1 Let X be any nonempty set and D be the set of all left continuous distribution functions. An
order pair (X, F) is called a non-Archimedean probabilistic metric space, if F is a mapping from X × X
Into D satisfying the following conditions
(i) F x , y(t) = 1 for every t > 0 if and only if x = y,
(ii) F x , y(0) = 0 for x, y ∈ X
(iii) F x , y(t) = F y , x(t) for every x, y ∈ X
(iv) If F x , y (t 1 ) = 1 and F y , z(t 2 ) = 1,
Then F x , z(max{t 1 , t 2 }) = 1 for every x, y, z ∈ X,
Definition 1.2 A Non- Archimedean Manger PM-space is an order triple (X, F, ∆ ), where ∆ is a t-norm
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Vol 1, No.1, 2011

and (X, F) is a Non-Archimedean PM-space satisfying the following condition.
(v) F x , z (max{ t ,t
1 2
} ≥ ∆ (F x , y ( t 1 ), F y , z( t 2
≥ 0.
)) for x,y,z ∈ X and t ,t
1 2
The concept of neighborhoods in Menger PM-spaces was introduced by Schwizer-Skla (1983). If x ∈ X, t >
0 and λ ∈ (0, 1), then and ( ∈, λ )-neighborhood of x, denoted by U x ( ε , λ ) is defined by
U x ( ε , λ ) = {y ∈ X : F y , x(t) > 1- λ }
If the t-norm ∆ is continuous and strictly increasing then (X, F, ∆ ) is a Hausdorff space in the topology
induced by the family {U x (t, y) : x ∈ X, t > 0, λ ∈ (0, 1)} of neighborhoods .
Definition 1.3 A t-norm is a function ∆ : [0, 1] × [0, 1] → [0, 1] which is associative,
commutative, non decreasing in each coordinate and ∆ (a, 1) = a for every a ∈ [0, 1].
Definition 1.4 A PM- space (X, F) is said to be of type (C) g if there exists a g ∈ Ω such that
g (F x , y(t)) ≤ g (F x , z(t)) + g (F z ,y(t))
for all x, y, z ∈ X and t ≥ 0, where Ω = {g : g [0,1] → [0, ∞ ) is continuous, strictly decreasing, g(1)
= 0 and g(0) > ∞ }.
Definition 1.5 A pair of mappings A and S is called weakly compatible pair if they commute at coincidence
points.
Definition 1.6 Let A, S: X → X be mappings. A and S are said to be compatible if
lim n→∞ g(FASx n , SAx n (t)) = 0
For all t > 0, whenever {x n } is a sequence in X such that lim n→∞ Ax n = lim n→∞ Sx n = z for some
z ∈ X.
Definition 1.7 A Non-Archimedean Manger PM-space (X, F, ∆ ) is said to be of type (D) g if there
exists a g ∈ Ω such that
g( ∆ (S, t) ≤ ∈ [0, 1].
g(S) + g(t)) for all S, t
Lemma 1.1 If a function φ : [0, + ∞ ) → [0,- ∞ ) satisfying the condition
( ∅ ), then we have

≥ 0, lim n→∞ φ (t) 0, where φ
n n
(1) For all t (t) is the n-th iteration of φ (t).

(2) If { t n
} is non-decreasing sequence real numbers and t n +1
≤ φ ( t n ), n = 1,2,….., then

lim n→∞ t n
= 0. In particular, if t ≤ φ (t) for all t ≥ 0, then t = 0.

Lemma 1.2 Let {y n } be a sequence in X such that lim n→∞ F y n
y n+1 (t) = 1 for all t > 0.

If the sequence {y n } is not a Cauchy sequence in X, then there exit ε0 > 0, t0 > 0, two sequences

{ mi }, { ni } of positive integers such that

(1) mi > ni +1, ni → ∞ as i → ∞ ,

(2) F y mi , y ni (t 0 ) < 1- ε0 and F y mi - 1, y ni (t 0 ) ≥ 1- ε 0 , i = 1,2,….
Main Results

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Vol 1, No.1, 2011

Theorem 2.1 : Let A, B, S, T, P and Q be a mappings from X into itself such that
(i) P(X) ⊂ AB(X), Q(X) ⊂ ST(X)
(ii) g(FPx, Qy(t)) ≤ φ [max{g(FABy, STx(t)), g(FPx, STx(t)), g(FQy, ABy(t)), g(FQy, STx(t)),
g(FPx, ABy(t))}]

(for all x, y ∈ X and t>0, where a function φ :[0,+ ∞ ) → [0,+ ∞ ) satisfies the condition ( ∅ ).
(iii) A(X) or B(X) is complete subspace of X, then
(a) P and ST have a coincidence point.
(b) Q and AB have a coincidence point.
Further, if
(iv) The pairs (P, ST) and (Q, AB) are R-weakly compatible then A,B,S,T,P and Q have a unique
common fixed point.
Proof: Since P(X) ⊂ AB(X) for any x0 ∈ X, there exists a point x1 ∈ X , Such that P x0 =AB x1 . Since
Q(X) ⊂ ST(X) for this point x1 ,we can choose a point x2 ∈ X such that B x1 =S x 2 and so on..
Inductively, we can define a sequence { yn } in X such that y2n =P x2n =AB x2 n+1 and
y2 n+1 =Q x2 n+1 =ST x2 n+ 2 , for n=1,2,3……..
Before proving our main theorem we need the following :
Lemma 2.2: Let A,B,S,T,P,Q :X → X be mappings satisfying the condition (i) and (ii).
Then the sequence { yn } define above, such that

lim g(F yn , yn+1 (t)) = 0, For all t>0 is a Cauchy sequence in X.
n→∞

Proof of Lemma 2.2: Since g ∈ Ω , it follows that

lim F yn , yn+1 (t) = 1 for all t>0 if and only if
n→∞

lim g(F yn , yn+1 (t)) = 0 for all t>0. By Lemma 1.2, if { yn } is not a Cauchy sequence in X,
n→∞

there exists ∈0 >0, t>0, two sequence { mi },{ ni }of positive integers such that

(A) mi > ni +1, and ni → ∞ as i → ∞ ,

(B) (Fy mi ,y ni ( t0 )) > g(1- ∈0 ) and g(Fy mi +1 ,y ni ( t0 )) ≤ g(1- ∈0 ), i=1,2,3……
Thus we have

g(1- ∈0 ) < (Fy mi ,y ni ( t0 ))

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≤ g(Fy mi , ymi−1 ( t0 )) + g(F ymi−1 ,y ni ( t0 ))

(v) ≤ g(1- ∈0 ) + g(F ymi , ymi−1 ( t0 ))

Thus i → ∞ in (v), we have

(vi) lim g(F ymi , y ni ( t0 )) = g(1- ∈0 ).
n→∞

On the other hand, we have

(vii) g(1- ∈0 ) < g(F ymi , y ni ( t0 ))

≤ g(F yni , yni+1 ( t0 ) ) + g(F yni+1 , ymi ( t0 ) ).

Now, consider g(F yni+1 , ymi ( t0 ) ) in (vii. Without loss generality, assume that both ni and mi are even.
Then by (ii), we have

g(F yni+1, ymi ( t0 )) = g(FP xmi , Q xni+1 ( t0 ))

≤ ∅ [max{g(FST xmi , AB xni+1 ( t0 )) , g(FST xmi , P xmi ( t0 )) , g(FAB xni+1 , Q xni+1 ( t0 )) ,

g(FST xmi , Q xni +1 ( t0 )) , g(FAB xni+1 , P xmi ( t0 ))}]

(viii) = ∅ [max{g(Fy mi−1 ,y ni ( t0 )), g(Fy mi −1 , y mi ( t0 )), g(Fy ni ,y ni+1 ( t0 )), g(Fy mi −1 ,y ni+1 ( t0 )),

g(Fy ni , y mi ( t0 )) }]

Using (vi),(vii),(viii) and letting i → ∞ n(viii), we have

g(1- ∈0 ) ≤ ∅ [max{g(1- ∈0 ), 0, 0, g(1- ∈0 ), g(1- ∈0 )}]

= ∅ (g(1- ∈0 ))

< g(1- ∈0 ),

This is a contradiction. Therefore {y n } is a Cauchy sequence in X.

Proof of the Theorem 2.1: If we prove lim n → ∞ g(Fy n , y ni+1 (t)) = 0 for all t>0, Then by Lemma(2.2)

the sequence {y n } define above is a Cauchy sequence in X.

Now, we prove lim n → ∞ g(Fy n , y n + 1 (t)) = 0 for all t > 0. In fact by (ii), we have

g(Fy 2 n , y 2 n+1 (t)) = g(FP X 2 n , Q X 2 n+1 (t))

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≤ ∅ [max {g(FST X 2n , AB X 2n , AB X 2 n+1 (t)), g(FST X 2n ,P X 2n (t)),

g(FAB X 2 n+1 , Q X 2 n+1 (t)), g(F X 2n , Q X 2 n +1 (t)), g(FAB X n +1 ,P X 2n (t))}]

= ∅ [max{g(Fy 2 n−1 , y 2n (t)), g(Fy 2 n−1 , y 2n (t)), g(Fy 2n ,y 2 n + 1 (t)),

g(Fy 2 n − 1 , y 2 n+1 (t))}],

= ∅ [max{g(Fy 2 n−1 , y 2n (t)), g(Fy 2 n−1 , y 2n (t)), g(Fy 2n ,y 2 n + 1 (t)),

g(Fy 2 n − 1 , y 2n (t)) + g(Fy 2n ,y 2 n + 1 (t)), 0}]

If g(Fy 2 n−1 , y 2n (t) ≤ g(Fy 2n ,y 2 n + 1 (t) for all t > 0, then we have

g(Fy 2n ,y 2 n + 1 (t)) ≤ ∅ g(Fy 2n ,y 2n ,y 2 n + 1 (t)),

Which means that,by Lemma 1.1, g(Fy 2n ,y 2 n + 1 (t)) = 0 for all t >0.

Similarly, we have g(Fy 2n ,y 2 n + 1 (t)) = 0 for all t > 0. Thus we have lim n → ∞ g(Fy n , y n + 1 (t)) = 0

for all t > 0. On the othr hand, if g(Fy 2 n − 1 , y 2n (t)) ≥ g(Fy 2n ,y 2 n + 1 (t)), then by (ii), we have

g(Fy 2n ,y 2 n + 1 (t)) ≤ g(Fy 2 n − 1 , y 2n (t)), for t > 0.

Similarly, g(Fy 2 n + 1 ,y 2 n+2 (t)) ≤ g(Fy 2n , y 2 n+1 (t)) for all t > 0 .

g(Fy n , y n + 1 (t)) ≤ g(Fy n − 1 ,y n (t)), for all t >0 and n= 1,2,3,…….
Therefore by Lemma (1.1)
lim n → ∞ g(Fy n , y n + 1 (t)) = 0 for all t > 0, which implies that {y n } is a Cauchy sequence in X.
Now suppose that ST(X) is a complete. Note that the subsequence {y n + 1 } is contained in ST(X) and a
−1
limit in ST(X) . Call it z. Let p ∈ (ST) z.

We shall use that fact that the subsequence {y 2 n } also converges to z. By (ii), we have

g(FP p , y 2 n+1 (kt)) = g(FP p ,Qx 2 n+1 (kt))

≤ ∅ [max{g(FST p , ABx 2 n+1 (t)), g(FST p , P p (t)), g(FAB x2 n+1 , Q x2 n+1 (t)),

g(FST p , Q x2 n+1 (t)), g(FAB x2 n+1 , P p (t))}]

= ∅ [max{FST p , y2 n (t),g(FST p ,P p (t)), g(F y2 n , y2 n+1 (t)), g(F ST p , y2 n+1 (t)), g(F y2 n , P p (t))}]

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Taking the limit n → ∞ , we obtain
g(FP p , z(kt)) ≤ ∅ [max{g(Fz, z(t)), g(Fz, P p (t)), g(Fz, z(t), g(Fz, z(t)), g(Fz, P p (t))}]

< ∅ (g(FP p , z(t))),

For all t>0,which means that P p = z and therefore, P p = ST p =z, i.e. p is a coincidence point of P
and ST. This proves (i). Since P(X) ⊂ AB(X) and , P p = z implies that z ∈ AB(X).
−1
Let q ∈ (AB) z. Then q = z.
It can easily be verified by using similar arguments of the previous part of the proof that Qq = z.
If we assume that ST(X) is complete then argument analogous to the previous completeness argument
establishes (i) and (ii).
The remaining two cases pertain essentially to the previous cases. Indeed, if B(X) is complete, then by (2.1),
z ∈ Q(X) ⊂ ST(X).
Similarly if P(X) ⊂ AB(X). Thus (i) and (ii) are completely established.
Since the pair {P, ST} is weakly compatible therefore P and ST commute at their coincidence point i.e.
PST p = STP p or Pz = STz. Similarly QABq = ABQq or Qz = ABz.
Now, we prove that Pz = z by (2.2) we have

g(FPz, y2 n+1 (t)) = g(FPz, Q x2 n+1 (t))

≤ ∅ [max{g(FSTz, AB x2 n+1 )), g(FSTz, Pz(t)), g(FAB x2 n+1 , Q x2 n+1 (t)),

g(FSTz , Q x2 n+1 (t)), g(FST x2 n+1 , Pz(t))}].

By letting n → ∞ , we have
g(FPz , z(t)) ≤ ∅ [max{g(FPz, z(t)), g(FPz, Pz(t)), g(Fz, z(t)), g(FPz, Pz(t)), g(Fz, Pz(t))}],
Which implies that Pz =z =STz.
This means that z is a common fixed point of A,B, S, T, P, Q. This completes the proof.
Acknowledgment: The author is thankful to the referees for giving useful suggestions and comments for
the improvement of this paper.
References
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Vol 1, No.1, 2011

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