WORDS COMMON

VOL. 16 NO. 4 (1993) 669-674

A COMMON FIXED POINT THEOREM OF MEIR AND KEELER TYPE

Y.J. CHO P.P.MURTHY G.JUNGCK

DepartmentofMathematics GyeongsangNational University

Jinju660-701, KOREA

Balajee GuestHouse Street-37, Sector-5 Bhilai(M.P.)490006,INDIA

DepartmentofMathematics BradleyUniversity Peoria, Illinois61625,U.S.A.

(Received

^June 10, 1992andin revisedform September 22,

1992))

ABSTRACT. In this paper, weintroduce theconcept of compatiblemappings oftype (A)^{on a} metricspace, which isequivalent to theconcept ofcompatiblemappings under^someconditions, and giveacommonfixed point theoremofMeirandKeeler type.

Our

result

extends,

generalized and improvessomeresults ofMeir-Keeler, Park-Bae,

Park-Rhoades,

Pantand

Rao-Rao,

etc.

1991AMS SUBJECT

CLASSIFICATION

CODE. 54H25.

KEY

WORDS AND PHRASES. Common fixed points, compatible mappings of type (A), generalized(e,6) {S,T}-contractions, and {S, T}-iterations.

1.

INTRODUCTION.

In [6],

Jungck proved a common fixed point theorem of commuting mappings on ametric space. Sincethen, he andmanyauthors extended, generalizedand unifiedthistheoremin many ways

([2], [4], [5], [7]-[10], [15]-[20], [22], [23]).

For example, Sessa

([22])introduced

the concept of weakly commuting mappings,which isageneralization of the conceptofcommuting mappings, and heand others provedsomefixedpoint theorems for weakly commuting mappings

([20]-[23]).

Recently, Jungck

([8])

proposed a generalization of the concept of weakly commuting mappings, whichis calledcompatible mappings, and hegeneralizedsomefixed point theorems of Meir-Keeler type, especially, ^atheorem of Park-Bae

([16]),

andin

[11], Jungck,

Murthy and Cho introduced the concept of compatible mappings oftype (A) on metric spacesandobtained some fixedpoint theorems for these mappings.

On the other hand, in

[14],

^Meir and Keeler established a fixed point theorem for a self- mappingf^ofametric space(X,d) satisfying thefollowingcondition:

Forevery >0, thereexistsa6>⁰suchthat

< d(z,V) < +6 implies d(fz, fv) <

. (1.1) In [13],

Maiti and Pal also proved a fixed point theorem for a self-mapping

I

^{of a metric}

spae(X,d)satisfying^thefollowingcondition,whichisageneralizationof

(1.1):

For

everye>0, thereexistsa 6>⁰such that

e<_rnaz{d(z,v),d(z,fz),d(y,fv)}<^e+6 implies _{d(fz, fv)}<

. ^(1.2)

In [17]

^and

[18],

Park-Rhoades and

RaRao

proved some fixed point theorems for self- mappings f^{and gofa}metric space (X,d)satisfying the following condition, respectively,which is ageneralization of

(1.2):

Foreverye>0, thereexistsa6>⁰suchthat

<_maz{d(fz,fy),d(fz, gz),d(fy,

gy),d(fz,

^{gy)+d(fy,gx))}<}

⁺

^{6 implies d(gz,gy)<e}

^(1.3)

Manyother fixed point theoremsof Meir-Keeler typearegivenin

[1], [3], IS], [12], [15], [16], [19]

^and

[21].

In

this paper, we introduce the concept of compatible mappings of type (A), which ^is equivalent to the concept ofcompatible mappings under some conditions, and give ^a common fixed point theorem for compatible mappings of type (A). which extends, generalizes and improvessomecommonfixedpoint theorems ofMeir-Keelertype.

2.

COMPATIBLE

MAPPINGS OF

TYPE (A).

In

this section, weshow that two pairs of compatiblemappingsandcompatible mappings of type (A) axeequivalent undersomeconditionsand give several properties of compatible mappings of type (A) forourmainresults. Throughoutthispaper,(X,d)denotes^ametric spce.

DEFINITION

2.1.

Let

S,T:(X,d)-.(X,d) be mappings. ^$and Taxesaid tobecompatibleif

imood(ST(n),TS(zn)

⁰

whenever{z,} ^isasequence in Xsuch that

ImooS(z,) T(z,,)

^{forsome in X.}

DEFINITION 2.2. LetS,T:(X,d)---,(X,d) bemappings. Sand Taxesaid to be compatible of type(A) if

lnimood(TS(zn),SS(zn)

^0and

ldrnood(ST(zn),

^{rT(zn) 0}

whenever {z,}^{isasequencein Xsuch that}

id._mooS(z,, IooT(z,,

^{forsome inX.}

’In [11],

^the following propositions show that Definitions 2.1 and 2.2 are equivalent under someconditions:

PROPOSITION

2.1. Let S,T X,d)-.(X,d) be continuous mappings. If S and T axe compatible, then theyaxecompatibleof type (A).

PROPOSITION2.2. Let$,T (X,d)-,(X,d) becompatiblemappings oftype(A). If^oneofS andT iscontinuous, then^$andTaxecompatible.

Thefollowingisadirectconsequence of Propositions2.1 and 2.2:

PROPOSITION 2.3. Let $,T: X,d)-,(X,d) be continuous mappings. Then S and T axe

compatibleifandonlyiftheyaxecompatibleoftype(A)

Thefollowing examples showthat Proposition 2.3 isnot true ifSandT axediscontinuousin somepoint ofX.

EXAMPLE

2.1. Let X R, theset of real numbers, with the usual metric d(z,y)=

Define S,T:(X, d)-(X, d)asfollows:

[r

^ifr#0,

$(z)

ifz=0

and Then S and T axe not continuous at =0.

n2,n

1,2,--.. Thenwe

have,

as n-oo,

and

but and

T(z)={z--2

if^ift=0.

^z’#0,

Consider a sequence

{r,,}

ⁱⁿ

x

defined by

so:.)

^0,

T(tn ^{1 O,}

n4

Id.rnd(ST(xn),

^TS(xn)

i.rnood(n4,

ⁿ

⁴⁾

⁰

md(ST(zn)’TT(zn)) mood(ns’n) moo ^{ns- n41}

^oo

Irnd(SS(zn),TS(zn) =/n/mcd(n:, n4) -/n/moo In n4l

^co.

Therefore,^SandTarecompatible butarenot compatibleof type(A).

EXAMPLE

2.2. LetX=[0,1]with the usualmetric d(x,u)= Ix-yl- Define$,T:[0,1 ]--.[0,1 by

{

^if

^[0,1/2),

^{and T(z)}

{:-r ^if[0,!)

S(z) ifz

[!

2’1] ifz

[1/2,1].

Then Sand Taxe not continuous at t=

1/2. ^Now,

^{weassert that S and Taxe not compatible but}

axe compatible ^of type (A).

To

see this, suppose that {r,}

_c

[0,1] ^{and that} T(z,,),S(r,,)--.t.

By

definition ofSand T,

{-,2

1}. Since ^$and Tagree^on

[1/2,1],

^{we needonly consider}

1/2. ^So

^we

can suppose that

r,,--

and that r, <

1/2

^{for all n. Then T(r,)=}

l-z,,--

^{from the right and}

s(r,)

r,--

^{fromthe left. Thus,since} r, >

,

^{for alln}

and,sincez,<

1/2,

Consequently, but

and

ST(xn) S(1 xn) TS(zn) T(zn)

r,t--"

d(ST(zn),TS(zn)

)-’

d(ST(z,,),TT(r.n)=

IST(r.)-TT(:,.,)I I1-T(1-r.)l

I1-

^I--,0 d(TS(rn),SS(zn) ITS(z,,)- SS(:,,) I(1 :,,)-r,, 2:,,

I-’0

as

r,,-.

^{Therefore,SandTare}compatible mappings of type (A) butarenotcompatible.

Next,

wegive several properties of compatible of type(A)forourmain theorems

([11]):

PROPOSITION 2.4. Let S, T: X,d)(X,d) be mappings. IfSand Tare compatibleof type (A) and S(t) T(t) forsome X, then ST(t) TT(t) TS(t) SS(t).

PROPOSITION 2.5. Let S,T: X,d)--,(X, d)be mappings. Let ^$andTbe compatible oftype (A) and let S(r,,), T(r,,)-,t for^some eX. Thenwehave thefollowing:

(1) /,,imooTS(r,,

^S(t)ifSis continuous att.

(2)

^{ST(t)=TS(t) and}S(t)= T(t) if^SandTaxecontinuous att.

PROOF. Immediate,from Proposition2.2and Proposition2.2

(2)

^of

[81

3.

A COMMON FIXED

POINT THEOREM.

Before stating and provingourmaintheorem,wegivesomedefinitionsandlemmas:

DEFINITION

3.1

([8]). ^Let

^{A,B,S and T be} mappings of a metric space (X,d) ^intoitself such that A(X) T(X) andB(X)C$(X). For

o

^{X, anysequence{v,,}definedby}

Y2n

Tz2n Az2n

2’

1 ^(3.1)

Y2n

SZ2n BZ2n-

for n 1,2,..-, iscalledan{S,T}-iteration^{ofz under}AandB.

Note

that Definition 3.1 assures us that {S,T}-iterations will exist since A(X)CT(X) and B(X)^CS(X),althoughthe sequence

{Yn}

^certainlyneed not be unique.

DEFINITION 3.2. Let A,B,S and T be mappings ofa metric space (X,d)intoitself. The pair {A,B}iscalledageneralized(,$)-{S,T}-contractionif

A(X)CT(X) and B(X)CS(X),

(3.2)

there^existsafunction&(0,oo)-(0,oo) suchthat,forany^e>⁰and (e) <

,

<_ maz{d(Sr,Ty),d(Sz, Az),d(Ty,

By),(d(Sr,

^By)+d(Ty,Az))} < ()

(3.3)

impliesd(Az,By)< for allz,y X.

Forourmaintheorem,firstwegive the following:

LEMMA

3.1. LetSandT bemappings ofametric space (X,d) intoitself and the pair {A,B}

beageneralized (,6)-{S,T}-contraction. If Zo ^Xand {y.} is an{$,T}-iteration of Zo under ^Aand B, thenwehave thefollowing:

(1)

for every >0, <

d(y,,yq)

< 6(e) implies

d(y,+

l,Yq+i)<

,

where

,

andqareofopposite parity.

(2) _m(R)d(n,y.

₊) ^O.

(3) {.}

^isaCauchysequencein X.

PROOF.

(1)

Since the pair {A,B}isageneralized(,)-{S,T}-contraction,forevery >^0,

<_maz{d(Sz,Ty),d(Sz, Az),d(Ty,

By),(d(Sz,

By)+d(Ty,Az))}< 6(f) implies d(Az,By)< for allz,y

.

^X.

Suppose

that <

d(yp, y)

<6(e). Putting p 2n and q 2m- in the above inequality, we have

and

d(yp+

1,Yq+1) d(Y2.₊1,Y2m) d(A::tn,

Bz2m-

¹⁾

<_

d(yp, yq)

d(Yan,Y2m_l) d(Sz2n’Tzam- 1)

<- maz(d{Sz2a, Tz2m-

1)’d(Sz2n’Az2n)’d(Tz2m 1’

Bz2m l)’(d(Sz2n’Bz2m-

1)

+

d(Tz:m-1’

Az2-))},

<6(), whichimpliesthat

d(y,+

1,Yq+l) d(Az2n, Bz:tm-l)<

"

(2)

For_Zo X, by

(3.3),

^wehave d(u.,

.

^{+ d(}

^Az.,

^Bz2,,

<maz{d(Sz2n,

Tza.-

)’d(Sz2n’Az2n)’d(Tz2.-

l’Bz2. l)’d(Sz2.’Bzan-

1)

+

d(Tzan-

, Aza.))}

{d(n,

yah l),d(y2n,yn+ 1), d(y.

1,yn),d(y2n,

y2.)

+

d(y2.__I’Y2.+

1))}

d(2. 1,Yah)"

Sillily,wehaved(u.₊l,Ua. +) < d(ua.,

a.

+).

Thus the

uen {d(y.,y.+

1)} ^isnon-increing dnvergto the

eatt

^{lower d =0}

of its rge rE0.

In

ft, other,

(1)

impH that d(y+,+)<t whenev Sd(y,u+)<6(t). But since {d(y,y+)} converg to t, there ests a t such that d(t, ut+

)<

6(t) d d(yt+

l,Yk+2)

< t, which

contracts

the

desiation

^{of t. Therefore, we}

have

d(y.,

_{y. +}

)

^0.

Theprf of

(3)

follows

om

the linmofthe prfof

mma

3.1

(c) ([8]). Ts

complet theprof.

Nowwe ereadyto prove o

mn

threm:

THEOM

3.2. t A,B,S d T mappings ofacomplete metc spe (X,d)intoit satisngtheconditions

(3.2),

(3.4)

^{oneofA,B,S, dT is}continuous,

(3.5)

^the

prs

A,Sd B,Tecompatible of ty (A)onX,

(3.6)

the pair {A,B} is a generalized (e,6)-{S,T}-contraction such that ^$ is lower semi- continuous.

ThenA,B,SandThaveauniquecommonfixedpoint in X.

PROOF. By

Lemma 3.1

(3),

^the {S,T}-iteration ofx under A and B, {y,}, ^{is a} Cauchy sequencein

x.

Since (X,d) iscomplete, {y,} converges toapoint in X. Since

{Sr,,} ^and {Tr2,_t} ^aresubsequencesof{y,}, they also convergetoz.

Suppose that S is continuous. Then wehave SS:2,,SAz,Sz ^asnoo. Since A and Sare

compatible of type (A), by Proposition 2.5

(1), ASz,-,Sz

^{as n-.oo.}

Now,

^we claim that Sz z.

Suppose Sz:/:^z and let M(x,V) ma{d(Sz,Tv),d(Sz,Ar),d(Tv,

Bv),(d(Sx,

Bv)+d(Tv, A:))}. If M,=M(Sz,,:2,_,), then ^we have M,,--..d(Sz,z)#^{0 asn---,oo.} Let e d(Sz,z) and remember that () > bydefinition. Since:(0,o)-.(0,o0)is lower semi-continuous, thereexists an a (0,)such that (t)>e ^for t(-a,+a). Choose to(-a,). Then wehave O<to<<,(to). But since M,--,^{as n--,o, thereexists an} integer n such that M, e. (to,,(to))^{for n}>_

no.

^{Therefore, by}

^(3.3),

wehave

d(ASz2,,Bz2,,_)< <^efor n>

no.

But d(ASz2n,Bz2n_)d(Sz,z)asn-oandsowehave d(Sz, z) < <

,

^{which isa}contradiction.

Tus

wehaveSz z.

We

also claim Az z.

Suppose

not and let d(Az, z)=

"

^and

^M,[=

^{M(z,z2,_). Thenwehave}

Mn’’as

^n---,o. Now duplicatetheargument usingthe lower semi-continuity of6toproducethe contradiction d(Az,z) <

’.

Thus we obtain Sz Az ^z. Since A(X)CT(X), there exists a point

w Xsuch thatz Sz Az Tw. Further,weclaimthatBw z. IfBw z, thenwehave d(z,Bw) d(Az, Bw)

<maz{d(Sz, Tw),d(Sz, Az),d(Tw,

Bw),1/2(d(Sz,

^Bw)

+

d(Tw,Az))}

d(z,Bw),

which is a contradiction. Hence Bw z Tw. Since B and T are compatible of type (A), by Proposition2.4, Bz BTw TTw Tz, thatis,Bz Tz.

Finally, weshallprovethatBz z. IfBz z, thenwehave d(z, Bz) d(Az, Bz)

< maz{d(Sz, Tz),d(Sz, Az),d(Tz,

Bz),d(Sz,

^{Bz) +d(Tz,Az))}}

=d(z,Bz),

which is a contradiction and so Bz ^z. Thus, zis acommon fixed point of A,B,S and T. The uniqueness of thecommonfixed pointzfollows easily from

(3.6).

Similarly, we can also completethe proofwhen A or Bor T is continuous. This completes theproof.

REMARK.

Theorem 3.2 extends, generalizes and improves ^{some results of} Chung

[3],

Jungck

[8],

^Maiti-Pal

[13],

Meir-Keeler

[14],

^Pant

[15],

^Park-Bae

[16],

Park-Rhoades

[17],

aao-Rao

[lS],

Rhoades

[19],

^etc.

REFERENCES

1.

ASSAD, N.A., A

fixedpointtheorem for weakly uniformly^strictcontractions, Canad. Math.

Bull. 16

(1) (1973),

^15-18.

2.

CHANG, S.S., A

commonfixedpoint for commuting mappings, Proc.Amer. Math. Soc. 83

(1981),

645-652.

3.

CHUNG, K.J.,

Onfixed point theorems of MeirandKePler, Math.

Japon.

24

(4) (1978),

381-383.

4.

DAS,

K.M.

& NAIK, K.V.,

Common fixed point theorems for commutingmaps on metric spaces,Proc.

Amer.

Math. Soc. 77

(1979),

^369-373.

5.

FISHER, B.,

Commonfixed points of commuting mappings, Bull. Inst. Math. Acad. Sinica 9 1981

),

399-406.

6.

JUNGCK, G.,

Commuting mappings and fixedpoints, Amer.Math. Monthly83

(1976),

261-263.

7.

JUNGCK, G.,

Periodicandfixed points,and commuting mappings, Proc. Amer. Math. Soc.

76

(1979),

^333-338.

8.

JUNGCK, G.,

Compatible mappings andcommonfixedpoints, Internat. J.Math.

&

^Math.

Sci. 9

(4) (1986),

^771-779.

9.

JUNGCK, G.,

Compatible mappings and common fixed points

(2),

^Internat.

^J.

^Math.

&

Math. Sci. 11

(1988),

^285-288.

10.

JUNGCK, G.,

Commonfixedpoints of commuting and compatiblemapsoncompacta,^Pro(:.

Amer.Math. Soc. 103

(1988),

977-983.

11.

JUNGCK, G.; MURTHY,

^P.P.

& CHO, Y.J.,

Compatible mappings oftype (A), to appear in Math.

Japon.

12.

KHAN, M.A.; KHAN,

M.S.

& SESSA, S.,

On a fixed point theorem of Rhoades in metricallyconvexspaces, Math.

Japon.

31

(1) (1986),

51-55.

13.

MAITI,

M.

& PAL, T.K.,

Generalizations oftwofixedpoint theorems,Bull. Calcutta Math.

Soc.

70

(1978),

^57-61.

14.

MEIR,

A.

& KEELER, E., A

theorem on contraction mappings, J. Math. Anal. Appl. 28 15.

PANT, R.P.,

Common fixed points oftwo pairs of commuting mappings, Indian J. Pure

Appl.Math. 17

(2) (1986),

^187-192.

16.

PARK,

S.

& BAE, J.S.,

Extensions of a fixed point theorem of Meir and KePler, Ark. Mat. 19

(1981),

223-228.

17.

PARK, S. & RHOADES, B.E.,

Meir-Keelertypecontractiveconditions, Math.

Japon.

26

(1) (1981),

^13-20.

18.

RAO,

I.H.N.

& RAO, K.P.R.,

Generalizations offixed point theorems of Meir and KePler type,Indian

J.

Pure hppl.Math. 16

(1) (1985),

^1249-1262.

19.

RHOADES, B.E., A

Meir and ^Kepler type fixed point theorem for three mappings, Jnanabha14

(1984),

^17-21.

20.

RHOADES,

B.E.

& SESSA, S.,

Commonfixed point theorems for three mappings under a weak commutativitycondition, IndianJ. PureAppl. Math. 17

(1986),

47-57.

21.

RHOADES, B.E.; PARK,

S.

& MOON, K.B.,

On generalizations of the Meir-Keeler type contraction maps,J. Math. Anal. Appl. 146

(1990),

482-494.

22.

SESSA, S.,

On a weak commutativitycondition of mappings in fixed point considerations, Publ.Inst. Math.32

(46) (1982),

^149-153.

23.

SINGH, S.L.; HA,

K.S.

& CHO, Y.J.,

Coincidence and fixed points of nonlinear Hybrid contractions,Internat. J. Math.

&

Math. Sci. 12

(1989),

^147-156.