VOL. 20 NO. 4 (1997) 681-688
LOCAL
CONNECTIVITY AND
MAPS ONTONON-METRIZABLE ARCS
J.NIKIEL
AmericanUniversity of Beirut Beirut, Lebanon [email protected]
and L.B. TREYBIG Texas
A & M
University CollegeStation,Texas 77843-3368,USAtreybigmath.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-scattered1991AMS 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 largerclassTiM
ofallrim-metrizable, locally connected continua. Namely,(1)
in[8]
in 1967 Mardeid proved that each element ofC has abasisofopenFa-sets
with metrizableboundaries, and(2)
in[4]
in 1991 Grispolakis, Nikiel, Simoneand Tymchatyn showed that ifa setP
is irreduciblewith respect tothe property of beingacompact setwhichseparates the elementX
ofC,
thenP
ismetrizable.Ihis 1989 thesis
[23]
andtwosubsequentpapers[24]
and[25]
Tuncalibegananinvestigation of the class7M
and continuousimages ofelements of that class. He showed that Treybig’s product theorem of[18]
which holdsin Cis nolonger valid inRM. However,
he provedthatMardeid’stheorem forConpreservationof weight by light mappingsis true in
RM, [25].
Healso consideredthe class
T.s
ofallrim-scattered, locally connectedcontinua, andtheclassRc
of alltim-countable, locallyconnected continua. Later,Nikiel, Tuncali andTymchatyn gavean exampletoshow that
R.c
is notasubclass oft?, [15].
Then,recently the authors ofthispaper showed thethe continuousimage ofanelement of7ZM
need not beinR.M, [14].
Furthermore, DrozdovskyandFilippovprovedin[3]
thatRs
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 letR.MN
denote the class of monotonicallynormal, locallyconnected continua. Ourfirstresult isth,
efollowing:THEOREM 1. If
X
EM
JS
U.MN
andfor each pairofpoints a, b EXthereexists acontinuousontomapf: X [c, d]
such thatf(a)
c,f(b)
d and[c, d]
isanon-metrizable arc, thenX
?.We
note that alargeclassof examples satisfying the properties ofX
above can becon- structedasfollows:In [1]
in1945Arens
studiedthe class oflinearhomogeneouscontinua, that isthe class ofarcswhich areorderisomorphictoeach oftheirsubarcs. Arens showed, thatup toahomeomorphism,thereexistatleastR1
membersof,
includingthe real numbersinterv[0,1].
Thus,somespacesX
asin Theorem 1 could beobtainedby pasting togethercopies of anyZ .
Ifasubset
B
ofaspaceP
containsnodense-in-itself, non-emptysubset,wesay thatB
is scattered.In
this paper the definitionofmonotone normality we use is anequivalent onegiven inLemma
2.2(a)
of[5]. It
says that a spaceP
is monotonically normalprovided there is an operatorG
which assigns toear
ordered pair(S, T)
ofmutually separated subsets ofP
an open setG(S, T)
such that(i)
SCG(S,T)
Ccl(G(S,T))
CP-T,
and(ii)
if(S’,T’)
is alsoa pair ofmutually separatedsets such that S CS’
andT’
CT,
thenG(S, T) c (S’, T’).
PROOF OF
THEOREM
1.Suppose
thatX
is nothereditarily locally connected. Then, thereexistsasubcontinuumC
ofX
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 inX
setscontainingp,andasequenceG1,G2, G3,... ofcontinuasuch that
(2)
G.R,#and G,R.+x =@
forn 1,2,3(3)
eachG, isacomponent ofU[3CandG,
(3bd(U) y
forn 1, 2,3,...;and(4) G.
f’lGm= 1
ifn rn, and there existmutuallyexclusive opensetsV1, V2,Vs,.
such that G,CV,,
forn 1,2,3,...Foreach positive integer n let H, be a component ofG,
R
which intersectsbd(Rl)
andbd(U),
andlet s.H.
Iqbd(R1)
and t, H, Nbd(U).
LetH0
denote the limiting set of the sequenceH,
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
xL2
so thatifVisaneighborhoodofs andWis aneighborhoodof t, then(s., t.)
belongsto VxWfor infinitelymanyn.Weshallshow that some component of
H0
contains s,}.
If not, thenH0
is theunionoftwomutually separatedsetsSand
T
suchthatsS
and T. Thereexistdisjoint open sets V andWsothat S CVandT
CW. Then(sn, t,)
belongs toV x Wfor infinitelymanyn.Sinceeach
H.
isacontinuum,H,
gl(X (V
UW)) 1
for infinitelymanyn. It follows that somepoint ofH0
lies inX (V
UW),
acontradiction.Let
f" X [c,d]
bea continuousmap ontoa non-metrizablearc[c,d],
wheref(s)
c andf(t)
d. Thereisanincreasingsequencenl, n2,n3 of positive integers such that(1) f(s.,) >_ f(s..+,)
andf(t.,) <_ f(t.,+,)
for 1,2,...;(2) f(s,.)
candf(t,,)
d; and(3) [f(s., ), f(t,,)]
isnotmetrizablefor 1,2Let
c’= f(snt)
andd’=f(t, t).
Our proofnowdivides intothreecases.
CASE 1.
X 7M. For
each n>
2 letM,
denote a metrizable closed set lying inX- Urn--1 Ht
such that if1< <
j<
n, thenH,
and Hj areselarated
inX
byM,. Let
D.
denoteacountablesetdenseinM,
forn 2, 3,... Weintend toshow thatf 0=2 Dr)
isdense 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 off-(]u,
vD
whichhavelimitpointsinbothf-(u)
andf-(v)
canbe labeledP,P2,...,P,o.
Let
No
be aninteger such that if>_ No
then s,,f-l([c,u[)
andt,, f-(]v,d]).
Thereexisttwo of
No,No +
1,...,No +
no, say and j,such thatHa.
andHa,
bothintersectthesamePt,
which mustthenintersectsomeD,.. Therefore,0=2 f(D)
intersects]u, v[.
CASE2.
X 7MN.
Foreaz.h 1,2,... let Qi denoteacomponent ofHn, CIf - ([c’,d’])
which intersects
f-(c’)
andf-(d’),
and let Q0 denote the limiting set ofQ,
Q2, Q3,... We note thatsomecomponentofQ0 intersectsbothf-(c’)
andf-l(d’)
sinceeverymap ontoanarcisweakly confluent.
By Remark 2.3
(c)
of[5], Z [,.J,__0 Q,,
is monotonicallynormal; so let beamonotone normality operatoronZ
asin the earlier definition. Foreach closed set F in[c ,
d]
letQ
F{x f(x)
6-F
and x 6- Z-Q0},
and letRF {x f(x)
6-[c’,d’]-
F and x 6-Q0}.
Now,
QF andRE
are mutually separated subsets ofZ;
so for each positive integer n, letT(F,n) {y
6_[c’,d’]
yf(x)
forsome x 6-Q, Cl(QF,RF)}.
It canbe shown that Tisstratificationfor
[c’, d’].
Since eachstratifiablecompact space ismetrizable,[c’, d’]
ismetrizable, acontradiction.CASE3.
X
6-Ts.
Foreach/=1,2,3,...letK,denoteacomponent ofH,. fir
-1([c’, d’])
which intersects
f-1 (c,)
andf-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 thata <
a2 implies thatda, < da2
in[c’, d’],
andda
d’.Let
K0
denote thelimitingsetof K1, K2, K3,... LetQ
denote acomponent ofK0
whichintersectsboth
f-(c’)
andf-(d’).
Foreacha<
Wl letWa
denoteaconnected open set such thatWa
containsapointXaofQclf-(]da, da+[),
andWa c f-(]da, do,+[).
There existsapositiveinteger
no
and acofinalsubsequence{dan }
ofda
such thatKn0 # @
forall a0. Foreach 7< wx
letL,
denote the closureof the set0_>, Wa.
LetL -<,01 Lv.
Observe that ify6-L,
then each openneighborhood ofy intersectsuncountably many setsWar.
Let Wbeacomponent ofL. NotethatWClK, # 0 #
QclWandWCf-(d’).
Thus,Wis anon-degeneratecontinuum.
Let
M0
andM1
be connectedopen setssuchthat00
NM---’" 0
andM,
ClW# 0
for 0,1.Let
{Mo, M }.
Nowsupposethat
,
hasbeen chosen and consistsof2 mutuallyexclusive connected open sets such that ifG,G’
q,
andG # G’,
thenC
’’7G1
and GClI # l # G’
NW.For
each
G’
6-,
letG
andG
bemutuallyexclusiveconnectedopen sets suchthat Go ClG1 GUG
C G’ andGW # 0 # G
W. Let,+ {F- F
G orF G
for someG’
6-g,}.
ForeachnletH: n
andlet H[n=l gn"
Thereexists$0
< w
such thatG’
Clf-(do
for eachG’
6-U= .
Thereexistsaclosedscattered set cin
X
whichseparatesf- ([c, d0]
fromf-(d’). However,
CglHcontains a perfect set because c ClH
can be mapped onto aCantor
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 localconnectivityofX
wefindthat for eachathereexistsonlyafinitenumber,sayha,of components off- (]ca, da[)
whichhavelimit points in bothf-(ca)
andf-l(d,,).
SomeintegerNo n=
repeats foruncountablymanya,’s;
sowemaysupposewithoutloss of generality thatn,,
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 setK,
where 1_< _< No +
hasthe property that somecomponent of
K,
Nf-l(]ca, d,[)
has limitpoints inbothf-’(ca)
andf-l(d,),
itfollows that Smust intersect eachf-1 (]ca, da[).
Since
[c’, d’]
isfirst countable,thereexist collections1,2,g3,--- such that(1)
eachconsists 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,,,
andletL’ --1L.
Wefindthat Sf-(L’)
containsaperfectset,acontradiction.
CASE 3B.
[c,d]
is not metrizable and does not contain uncountably many mutually exclusiveopen sets(i.e.,
itisaSouslinline).
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’]
weletnz
denote the numberofcomponents off-(]z,y[)
with limit points in bothf-(x)
andf-(y).
CASE
3B. Suppose
thereexistsapositive integerNo
and asubintervalIx, y[
ofsuch that ifx
_<
z<
w_<
y, then n,_< No.
Let S be aclosed scatteredset such that if 1_< <
j_< No +
1, thenSseparatesK,
fromKj. Usingthe ideasfromCase3A
we findthatifx
_<
z<
w_<
y, then S]’-(]z, w[) # .
Therefore,f(,.S)
:3Ix, y],
which contradicts the well-known fact thatascattered compactumcannotbemappedontoaperfect set.CASE
3B2.
Assumethat foreveryIx, y[
C[c’, d’]
thereexistsaninterval]z, w[
CIx, y[
such thatn,o> n=.
Foreach positiveintegernlet
,,
be maximal relativetothepropertyofbeingacollection of mutuallyexclusive open intervalslyingin[d, d’]
suchthatifIx, y[ ,,
thennffi n. Notethat each,,
isat mostcountable. LetS,,
denote thesetof all end-points ofintervalswhichbelong to,,. We
aregoingtoshowthatU,,__ Sn
isdensein[c’, d’],
and thus obtainacontradiction.Let
Ix, y[
C[d, d].
Thereexists]z, w[
CIx, y[
such thatn > nz.
Thus,x#
z ory#
w.By
maximality of,,,,
thereexistsIs, t[ e ,,,
such that]s, t[
g]z, w[ #
}. ButIs, t[ ]x, y[,
andso se Ix, y[
ore Ix, y[.
Therefore,thesetU,,__ 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)
everysubcontinuumG
ofX
has the property thatsomepointorapair of points separatesG,
and(c)
eachclosedset irreducible with respect tothe property ofbeingacompactsetwhich sepa- ratesX
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, bofX
letIX,
a,b]
denote the class of all continuous maps
f X
P such that Pf(X)
is anon-metricarcwithend-pointsc anddand
f(a)
candf(b)
d. Also,introducearelation onX
in the followingway: a b ifand onlyifa bor[X,
a,b] .
THEOREM 3.
Suppose
thatX
is alocally connectedcontinuum. Then isanequiv- alence relationonX,
and ifX
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
EIX,
a,c]
suchthatf(X)
is anon-metricarc[d, e]
withf(a)
dand
f(c)
e.CASE 1.
f(b)
d. Thenf
EIX,
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)]
andr(z) f(b)
ifzIf(b), el.
Clearly, rof . [X,a, hi,
acontradiction.Letusnowshow that each equivalence classG
andsuppose thatx E
-
G. ThereexistsacountablebasisU1,U,...
ofopenneighborhoods of x inX
and a sequencex,z2,.., of points of G such that x, U, for 1,2,... Letf" X
--,[c,d]
beacontinuous map ontoanon-metricarc[c,d],
wheref(zl)
candf(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. LettheelementG
of’
beasubsetofanopen setU. Suppose
thatfor each open setV
suchthatG
CV
CU,
there isanelementGv
of sothat VIqGv l
andGv . U.
Thus, forsome pointx ofG
thereisa countablebasis
U, U,...
ofopenneighborhoodsof zsuch that for eachU,
thereisanelement
G,
of"
withtheproperty thatG,
fqU,
}Gi
tq(X U).
There is a pointy of
X U
sothat everyneighborhood of y intersectsGi
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, EUi
f’lG,for 1,2,...Thereexists
f [X,z, y]
such thatf X [c,d],
where[c, d]
isanon-metric arc,f(x)
c andf(y) d. Since the pointsf(z,)
convergeto c,andthepointsf(yi)convergetod,andeach arcIf(z,), f(y,)]
ismetric,wefindthat[c,d]
is metric acontradiction.THEOREM 4. SupposethatXE
’’M
[..J’S
[,..JTMN
andXisfirstcountable. Let be the family of allcomponentsofsetsin’. ThenX/TI
isthecontinuousimage ofan arc.PROOF. Since
c
is uppersemi-continuous, 7"/isupper semi-continuousas well(see
e.g.[28]).
Thus,7isaupper semi-continuous decomposition ofX
intoclosed sets and the quotient spaceX/TI
isalocallyconnected continuum.If
X/TI
is hereditarilylocally connected, we apply the main result of[12]
to obtain thedesired conclusion.
Otherwise,in
X/7"t
there isasubcontinuumCsuch thatCfails to beconnectedim kleinen at apoint P. Thereis thus anopen set WinX/7"I
such thatP
E Wbut the component of WNCcontainingPcontainsnorelatively open subset ofC containingP. LetQ
denote the element ofc
containing P. Thereis aclosed subset SofX
such that S C[J
W-Q
and S separatesP
frombd([J W)
inX. Let :XX/7"I
denote thenatural mapand letB (S).
Let
U
denote the component ofX/TI- B
which containsP. Using the factsthat is upper semi-continuousand thatQ
NS},
weletR1, R2,... G1, G2,...V, V2
be subsets ofX/7"I
,similarlyasinthe proof of Theorem 1, except for theadditional conditionthatnoelement of intersectscl([,J R)
andbd([,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,... SinceX
isfirstcountable, wemayassumewithoutlossof generality that thepoints s, convergetosomepoints,andthe pointst, convergetosomepointt,and the limitingsetL
of[.J G, U G,
G3, isacontinuumcontainingsandt.Thereisan
f e [X,s,t]
such thatf(X)is
anon-metric arc[c,d]
withf(s)
candf(t)
d.Wemaynowobtainacontradictionasinthe proof of Theorem 1.
ACKNOWLEDGMENT. H.M.Tuncali waspartially supported byan
NSREC
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