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(1)

VOL. 20 NO. 4 (1997) 681-688

LOCAL

CONNECTIVITY AND

MAPS ONTO

NON-METRIZABLE ARCS

J.NIKIEL

AmericanUniversity of Beirut Beirut, Lebanon [email protected]

and L.B. TREYBIG Texas

A & M

University CollegeStation,Texas 77843-3368,USA

treybigmath.tamu.edu and

H.M.TUNCALI NipissingUniversity

NorthBay, Ontario, Canada P1B 8L7 murat einstein.unipissing,ca

(Received December 15, 1995 and in revised form July 6, 1996)

ABSTRACT.Threeclasses of locallyconnected continua which admitsufficientlymanymaps ontonon-metricarcs areinvestigated. Itisproved that allcontinuainthose classesarecontin- uousimages ofarcsand,therefore,have other quiteniceproperties.

KEY

WORDSAND PHRASES: arc,locally connected continuum,monotonicallynormal, rim-countable, rim-finite, rim-metrizable,rim-scattered

1991AMS SUBJECT CLASSIFICATION CODES: Primary54F15, Secondary 54C05 54F05

INTRODUCTION

Let

C

denote the class of allHausdorif continuousimages of orderedcontinua.

In

the last three decades the class C has been studied extensivelyby a number of authors

(see

e.g.

[2],

[4], [6-8], [11-13], [16-22], [26]

and

[27]).

Two results fromthisstudy havesuggested that the investigation couldnaturally be extended tothe largerclass

TiM

ofallrim-metrizable, locally connected continua. Namely,

(1)

in

[8]

in 1967 Mardeid proved that each element ofC has abasisofopen

Fa-sets

with metrizableboundaries, and

(2)

in

[4]

in 1991 Grispolakis, Nikiel, Simoneand Tymchatyn showed that ifa set

P

is irreduciblewith respect tothe property of beingacompact setwhichseparates the element

X

of

C,

then

P

ismetrizable.

(2)

Ihis 1989 thesis

[23]

andtwosubsequentpapers

[24]

and

[25]

Tuncalibegananinvestigation of the class

7M

and continuousimages ofelements of that class. He showed that Treybig’s product theorem of

[18]

which holdsin Cis nolonger valid in

RM. However,

he provedthat

Mardeid’stheorem forConpreservationof weight by light mappingsis true in

RM, [25].

He

also consideredthe class

T.s

ofallrim-scattered, locally connectedcontinua, andtheclass

Rc

of alltim-countable, locallyconnected continua. Later,Nikiel, Tuncali andTymchatyn gavean exampletoshow that

R.c

is notasubclass of

t?, [15].

Then,recently the authors ofthispaper showed thethe continuousimage ofanelement of

7ZM

need not bein

R.M, [14].

Furthermore, DrozdovskyandFilippovprovedin

[3]

that

Rs

isalargerclass of spaces than/Zc.

Also, in 1973 Heath, Lutzer and

Zenor, [5],

showed that every linearly ordered ordered topologic space and each of its Hausdorffcontinuous and closed images aremonotonically normal.

In [10]

in1986Nikielaskedifevery monotonically normal compactumisthecontinuous image ofacompact ordered space. That problem still remainsopen.

In

what follows we let

R.MN

denote the class of monotonicallynormal, locallyconnected continua. Ourfirstresult is

th,

efollowing:

THEOREM 1. If

X

E

M

J

S

U

.MN

andfor each pairofpoints a, b EXthereexists acontinuousontomap

f: X [c, d]

such that

f(a)

c,

f(b)

d and

[c, d]

isanon-metrizable arc, then

X

?.

We

note that alargeclassof examples satisfying the properties of

X

above can becon- structedasfollows:

In [1]

in1945

Arens

studiedthe class oflinearhomogeneouscontinua, that isthe class ofarcswhich areorderisomorphictoeach oftheirsubarcs. Arens showed, thatup toahomeomorphism,thereexistatleast

R1

membersof

,

includingthe real numbersinterv

[0,1].

Thus,somespaces

X

asin Theorem 1 could beobtainedby pasting togethercopies of any

Z .

Ifasubset

B

ofaspace

P

containsnodense-in-itself, non-emptysubset,wesay that

B

is scattered.

In

this paper the definitionofmonotone normality we use is anequivalent onegiven in

Lemma

2.2

(a)

of

[5]. It

says that a space

P

is monotonically normalprovided there is an operator

G

which assigns to

ear

ordered pair

(S, T)

ofmutually separated subsets of

P

an open set

G(S, T)

such that

(i)

SC

G(S,T)

C

cl(G(S,T))

CP-

T,

and

(ii)

if

(S’,T’)

is alsoa pair ofmutually separatedsets such that S C

S’

and

T’

C

T,

then

G(S, T) c (S’, T’).

PROOF OF

THEOREM

1.

Suppose

that

X

is nothereditarily locally connected. Then, thereexistsasubcontinuum

C

of

X

such that Cfails tobe connectedim kleinen at thepoint p. Utilizingtheideas inTheorem 11, p. 90,ofMoore

[9],

there existsaconnectedopenset U containingp,asequenceR1, R2,R3,...of connected open in

X

setscontainingp,andasequence

(3)

G1,G2, G3,... ofcontinuasuch that

(2)

G.R,

#and G,R.+x =@

forn 1,2,3

(3)

eachG, isacomponent ofU[3Cand

G,

(3

bd(U) y

forn 1, 2,3,...;and

(4) G.

f’l

Gm= 1

ifn rn, and there existmutuallyexclusive opensetsV1, V2,

Vs,.

such that G,C

V,,

forn 1,2,3,...

Foreach positive integer n let H, be a component ofG,

R

which intersects

bd(Rl)

and

bd(U),

andlet s.

H.

Iq

bd(R1)

and t, H, N

bd(U).

Let

H0

denote the limiting set of the sequence

H,

H2,H3,...; whichby definitionis theset ofall x such thateveryopen set containingx intersectsinfinitely manysetsH,.

Let

L

(resp.

L2)denote

the limitingset of

{sl}, {s2}, {3},

(resp.

{t}, {t2}, {t3}, ...).

Thereexists

(s, t) L

x

L2

so thatifVisaneighborhoodofs andWis aneighborhoodof t, then

(s., t.)

belongsto VxWfor infinitelymanyn.

Weshallshow that some component of

H0

contains s,

}.

If not, then

H0

is theunionof

twomutually separatedsetsSand

T

suchthats

S

and T. Thereexistdisjoint open sets V andWsothat S CVand

T

CW. Then

(sn, t,)

belongs toV x Wfor infinitelymanyn.

Sinceeach

H.

isacontinuum,

H,

gl

(X (V

U

W)) 1

for infinitelymanyn. It follows that somepoint of

H0

lies in

X (V

U

W),

acontradiction.

Let

f" X [c,d]

bea continuousmap ontoa non-metrizablearc

[c,d],

where

f(s)

c and

f(t)

d. Thereisanincreasingsequencenl, n2,n3 of positive integers such that

(1) f(s.,) >_ f(s..+,)

and

f(t.,) <_ f(t.,+,)

for 1,2,...;

(2) f(s,.)

cand

f(t,,)

d; and

(3) [f(s., ), f(t,,)]

isnotmetrizablefor 1,2

Let

c’= f(snt)

andd’=

f(t, t).

Our proofnowdivides intothreecases.

CASE 1.

X 7M. For

each n

>

2 let

M,

denote a metrizable closed set lying in

X- Urn--1 Ht

such that if1

< <

j

<

n, then

H,

and Hj are

selarated

in

X

by

M,. Let

D.

denoteacountablesetdensein

M,

forn 2, 3,... Weintend toshow that

f 0=2 Dr)

is

dense in

[c, d],

whichwouldmeanthat

[c, d]

isseparable, and therefore metric,acontradiction.

Let x(5

]c, d[

andlet c

<

u

<

x

<

v

<

din the natural ordering of

[c, d].

The components of

f-(]u,

v

D

whichhavelimitpointsinboth

f-(u)

and

f-(v)

canbe labeledP,P2,...

,P,o.

Let

No

be aninteger such that if

>_ No

then s,,

f-l([c,u[)

and

t,, f-(]v,d]).

There

existtwo of

No,No +

1,...

,No +

no, say and j,such that

Ha.

and

Ha,

bothintersectthesame

Pt,

which mustthenintersectsomeD,.. Therefore,

0=2 f(D)

intersects

]u, v[.

CASE2.

X 7MN.

Foreaz.h 1,2,... let Qi denoteacomponent of

Hn, CIf - ([c’,d’])

which intersects

f-(c’)

and

f-(d’),

and let Q0 denote the limiting set of

Q,

Q2, Q3,... We note thatsomecomponentofQ0 intersectsboth

f-(c’)

and

f-l(d’)

sinceeverymap ontoan

arcisweakly confluent.

(4)

By Remark 2.3

(c)

of

[5], Z [,.J,__0 Q,,

is monotonicallynormal; so let beamonotone normality operatoron

Z

asin the earlier definition. Foreach closed set F in

[c ,

d

]

let

Q

F

{x f(x)

6-

F

and x 6- Z-

Q0},

and let

RF {x f(x)

6-

[c’,d’]-

F and x 6-

Q0}.

Now,

QF and

RE

are mutually separated subsets of

Z;

so for each positive integer n, let

T(F,n) {y

6_

[c’,d’]

y

f(x)

forsome x 6-

Q, Cl(QF,RF)}.

It canbe shown that Tis

stratificationfor

[c’, d’].

Since eachstratifiablecompact space ismetrizable,

[c’, d’]

ismetrizable, acontradiction.

CASE3.

X

6-

Ts.

Foreach/=1,2,3,...letK,denoteacomponent of

H,. fir

-1

([c’, d’])

which intersects

f-1 (c,)

and

f-1 (d’).

Wehavetoconsider some subcases.

CASE 3A.

[c’, d’]

containsuncountablymanymutuallyexclusive open sets.

CASE

3A1. [c’,d’]

does notsatisfy thefirst axiomof countability. Thus,withoutlossof generality,assumethat there isasubset

{da

a

< w

of

[c’, d’]

such that

a <

a2 implies that

da, < da2

in

[c’, d’],

and

da

d’.

Let

K0

denote thelimitingsetof K1, K2, K3,... Let

Q

denote acomponent of

K0

which

intersectsboth

f-(c’)

and

f-(d’).

Foreacha

<

Wl let

Wa

denoteaconnected open set such that

Wa

containsapointXaofQcl

f-(]da, da+[),

and

Wa c f-(]da, do,+[).

There existsapositiveinteger

no

and acofinalsubsequence

{dan }

of

da

such that

Kn0 # @

forall a0. Foreach 7

< wx

let

L,

denote the closureof the set

0_>, Wa.

Let

L -<,01 Lv.

Observe that ify6-

L,

then each openneighborhood ofy intersectsuncountably many sets

War.

Let Wbeacomponent ofL. Notethat

WClK, # 0 #

QclWandWC

f-(d’).

Thus,Wis anon-degeneratecontinuum.

Let

M0

and

M1

be connectedopen setssuchthat

00

N

M---’" 0

and

M,

ClW

# 0

for 0,1.

Let

{Mo, M }.

Nowsupposethat

,

hasbeen chosen and consistsof2 mutuallyexclusive connected open sets such that if

G,G’

q

,

and

G # G’,

then

C

’’7G

1

and GCl

I # l # G’

NW.

For

each

G’

6-

,

let

G

and

G

bemutuallyexclusiveconnectedopen sets suchthat Go Cl

G1 GUG

C G’ and

GW # 0 # G

W. Let

,+ {F- F

G or

F G

for some

G’

6-

g,}.

Foreachnlet

H: n

andlet H

[n=l gn"

Thereexists$0

< w

such that

G’

Cl

f-(do

for each

G’

6-

U= .

Thereexistsa

closedscattered set cin

X

whichseparates

f- ([c, d0]

from

f-(d’). However,

CglHcontains a perfect set because c Cl

H

can be mapped onto a

Cantor

set, and it is wellknown that a scatteredsetcannotbemappedcontinuouslyonto aperfect set. Thisisa contradiction.

CASE

3A2. [c’, d’]

satisfiesthefirst axiomof countability ateach point. Let

{]ca,

a

< w }

denoteanuncountablecollection ofmutuallyexclusive open intervals in

]c’, d’[.

Using the localconnectivityof

X

wefindthat for eachathereexistsonlyafinitenumber,sayha,of components of

f- (]ca, da[)

whichhavelimit points in both

f-(ca)

and

f-l(d,,).

Someinteger

No n=

repeats foruncountablymany

a,’s;

sowemaysupposewithoutloss of generality that

(5)

n,,

No

for eacha

<

w.

Thereexists aclosed scattered set Ssuch thatS separates

K,

from Kj for each pairi, such that 1

_< <

j

_< No +

1. Thus,sinceforeach a, each set

K,

where 1

_< _< No +

has

the property that somecomponent of

K,

N

f-l(]ca, d,[)

has limitpoints inboth

f-’(ca)

and

f-l(d,),

itfollows that Smust intersect each

f-1 (]ca, da[).

Since

[c’, d’]

isfirst countable,thereexist collections1,2,g3,--- such that

(1)

each

consists of 2 mutually exclusive closed intervals in

[c’,d’],

and

(2)

each element of each containsexactly two elements of,,+1 and containsuncountably many elements of

{]ca,d[:

<wl}.

Foreachpositiveintegernlet

L’, [.J,,,

andlet

L’ --1L.

Wefindthat S

f-(L’)

containsaperfectset,acontradiction.

CASE 3B.

[c,d]

is not metrizable and does not contain uncountably many mutually exclusiveopen sets

(i.e.,

itisaSouslin

line).

Thus,

[c’, d’]

satisfiesthefirst axiomof countability.

If thereexists acollectionof metrizable open intervals whoseunion isdense in

[c , d],

wefind that

[c’,

d

]

ismetrizable since it isseparable.

Hence,

withoutloss of generalitywemay assume that

[c , d’]

containsnometrizablesubinterval.

Similarlyasabove, for each

Ix, y[

C

[d, d’]

welet

nz

denote the numberofcomponents of

f-(]z,y[)

with limit points in both

f-(x)

and

f-(y).

CASE

3B. Suppose

thereexistsapositive integer

No

and asubinterval

Ix, y[

of

such that ifx

_<

z

<

w

_<

y, then n,

_< No.

Let S be aclosed scatteredset such that if 1

_< <

j

_< No +

1, thenSseparates

K,

fromKj. Usingthe ideasfromCase

3A

we findthat

ifx

_<

z

<

w

_<

y, then S

]’-(]z, w[) # .

Therefore,

f(,.S)

:3

Ix, y],

which contradicts the well-known fact thatascattered compactumcannotbemappedontoaperfect set.

CASE

3B2.

Assumethat forevery

Ix, y[

C

[c’, d’]

thereexistsaninterval

]z, w[

C

Ix, y[

such thatn,o

> n=.

Foreach positiveintegernlet

,,

be maximal relativetothepropertyofbeingacollection of mutuallyexclusive open intervalslyingin

[d, d’]

suchthatif

Ix, y[ ,,

thennffi n. Notethat each

,,

isat mostcountable. Let

S,,

denote thesetof all end-points ofintervalswhichbelong to

,,. We

aregoingtoshowthat

U,,__ Sn

isdensein

[c’, d’],

and thus obtainacontradiction.

Let

Ix, y[

C

[d, d].

Thereexists

]z, w[

C

Ix, y[

such that

n > nz.

Thus,x

#

z ory

#

w.

By

maximality of

,,,,

thereexists

Is, t[ e ,,,

such that

]s, t[

g

]z, w[ #

}. But

Is, t[ ]x, y[,

andso s

e Ix, y[

or

e Ix, y[.

Therefore,theset

U,,__ s,,

isdensein

[c’, d’],

acontradiction.

Theconsiderationof subcases 1, 2 and 3isconcluded andwereturn now tothemainproof.

Since

X

ishereditarily locallyconnected,it isthecontinuousimage ofanarcby

[12].

THEOREM 2. If

X

isasinTheorem1,then

(a) X

isrim-finite,

(b)

everysubcontinuum

G

of

X

has the property thatsomepointorapair of points separates

G,

and

(6)

(c)

eachclosedset irreducible with respect tothe property ofbeingacompactsetwhich sepa- rates

X

is metrizable.

PROOF.Theclaims

(a), (b)

and

(c)

followfrom

[19], [18]

and

[4],

respectively, because Xcontainsnonon-degeneratemetric continuum.

Givenalocally connectedcontinuum

X,

for each pairofdistinct points a, bof

X

let

IX,

a,

b]

denote the class of all continuous maps

f X

P such that P

f(X)

is anon-metricarc

withend-pointsc anddand

f(a)

cand

f(b)

d. Also,introducearelation on

X

in the followingway: a b ifand onlyifa bor

[X,

a,

b] .

THEOREM 3.

Suppose

that

X

is alocally connectedcontinuum. Then isanequiv- alence relationon

X,

and if

X

also satisfiesthe first axiom ofcountability, then equivalence classesof areclosed and theset

of equivalenceclassesof is upper semi-continuous.

PROOF. iseasilyseentobe reflexive and symmetric,sosupposethata b and b c

hold,but thatthereexists

f

E

IX,

a,

c]

suchthat

f(X)

is anon-metricarc

[d, e]

with

f(a)

d

and

f(c)

e.

CASE 1.

f(b)

d. Then

f

E

IX,

b,

c],

acontradiction.

CASE 2.

f(b)

e analogoustoCase1.

CSE 3. d

<

y(b)

< . T

o oft5

[d,y(b)]

d

[y(b),]

is non-mettle, so suppose

[d, f(b)]

isnon-mettle. Define r

"[d,e] [d, y(b)]

othat

()

if xE

[d, f(b)]

and

r(z) f(b)

ifz

If(b), el.

Clearly, ro

f . [X,a, hi,

acontradiction.

Letusnowshow that each equivalence classG

andsuppose thatx E

-

G. ThereexistsacountablebasisU1,

U,...

ofopenneighborhoods of x in

X

and a sequencex,z2,.., of points of G such that x, U, for 1,2,... Let

f" X

--,

[c,d]

beacontinuous map ontoanon-metricarc

[c,d],

where

f(zl)

cand

f(z)

d.

Since each

[y(),y(z)]

is a metric subarc of

[c,d],

it follows that

[c,d]

is the closure ofa countable unionofmettleares. Consequently,

[c,d]

is separable, and therefore mettlzable, a contradiction. ThusGisclosedinX.

Itremainstoshow that is upper semi-continuous if

X

isfirstcountable. Lettheelement

G

of

beasubsetofanopen set

U. Suppose

thatfor each open set

V

suchthat

G

C

V

C

U,

there isanelement

Gv

of sothat VIq

Gv l

and

Gv . U.

Thus, forsome pointx of

G

thereisa countablebasis

U, U,...

ofopenneighborhoodsof zsuch that for each

U,

thereis

anelement

G,

of

"

withtheproperty that

G,

fq

U,

}

Gi

tq

(X U).

There is a pointy of

X U

sothat everyneighborhood of y intersects

Gi

for infinitely many i. Wemay assume withoutloss of generality that thereexists y, G,[q

(X U)

for each i, and that the pointsyi convergeto y. Letz, E

Ui

f’lG,for 1,2,...

Thereexists

f [X,z, y]

such that

f X [c,d],

where

[c, d]

isanon-metric arc,

f(x)

c andf(y) d. Since the points

f(z,)

convergeto c,andthepointsf(yi)convergetod,andeach arc

If(z,), f(y,)]

ismetric,wefindthat

[c,d]

is metric acontradiction.

(7)

THEOREM 4. SupposethatXE

’’M

[..J

’S

[,..J

TMN

andXisfirstcountable. Let be the family of allcomponentsofsetsin’. Then

X/TI

isthecontinuousimage ofan arc.

PROOF. Since

c

is uppersemi-continuous, 7"/isupper semi-continuousas well

(see

e.g.

[28]).

Thus,7isaupper semi-continuous decomposition of

X

intoclosed sets and the quotient space

X/TI

isalocallyconnected continuum.

If

X/TI

is hereditarilylocally connected, we apply the main result of

[12]

to obtain the

desired conclusion.

Otherwise,in

X/7"t

there isasubcontinuumCsuch thatCfails to beconnectedim kleinen at apoint P. Thereis thus anopen set Win

X/7"I

such that

P

E Wbut the component of WNCcontainingPcontainsnorelatively open subset ofC containingP. Let

Q

denote the element of

c

containing P. Thereis aclosed subset Sof

X

such that S C

[J

W-

Q

and S separates

P

from

bd([J W)

inX. Let :X

X/7"I

denote thenatural mapand let

B (S).

Let

U

denote the component of

X/TI- B

which containsP. Using the factsthat is upper semi-continuousand that

Q

NS

},

weletR1, R2,... G1, G2,...

V, V2

be subsets of

X/7"I

,similarlyasinthe proof of Theorem 1, except for theadditional conditionthatnoelement of intersects

cl([,J R)

and

bd([,J U). ’

Now, lets,s2,.., and t,t2,.., be such that s, E

([.J

G,)g

(Ubd(R1))

andt, E

(UG,) ( bd(U))

for 1, 2,... Since

X

isfirstcountable, wemayassumewithoutlossof generality that thepoints s, convergetosomepoints,andthe pointst, convergetosomepointt,and the limitingset

L

of

[.J G, U G,

G3, isacontinuumcontainingsandt.

Thereisan

f e [X,s,t]

such that

f(X)is

anon-metric arc

[c,d]

with

f(s)

cand

f(t)

d.

Wemaynowobtainacontradictionasinthe proof of Theorem 1.

ACKNOWLEDGMENT. H.M.Tuncali waspartially supported byan

NSREC

grant.

REFERENCES

[1] Arens, R.,

"Ontheconstructionoflinearhomogeneouscontinua,"

Bl.

Soc. Mat. Mezicana 2

(1945),

33-36.

[2] Cornette, J.L., "Image

ofa Hausdorffarc is cyclically extensible and reducible," Trans.

Amer.

Math.

Soc.

199

(1974),

255-267.

[3]

Drozdovsky

S.A.

and Filippov,

V.V., "An

example of a rim-scattered locally connected- continuura which is not rim-countable

(in

Russian)," Mat. Sbornik 185, No. 10

(1994),

27-38.

[4]

Grispolakis,

J.,

Nikiel,

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