Convergence of Probability Measures 
WILEY SERIES IN PROBABILITY AND STATISTICS 
PROBABILITY AND STATISTICS SECTION 
Established by WALTER A. SHEWHART and SAMUEL S. WILKS 
Editors: Vic Barnett, Noel A. C. Cressie, Nicholas I. Fisher, 
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Bernard  W. Silverman, Adrian F. M. Smith, Jozef L. Teugels; 
Ralph A. Bradley, Emeritus, J. Stuart Hunter, Emeritus 
A complete list of the titles in this series appears at the end of this volume. 
Convergence of 
Probability Measures 
Second Edition 
PATRICK BILLINGSLEY 
TEe University of Chicago 
Chicago, Illinois 
A Wiley-Interscience Publication 
JOHN WILEY & SONS, INC. 
NewYork  Chichester  Weinheim  Brisbane 
Singapore  Toronto 
This text is printed on acid-free paper.  8 
Copyright 0 1999 by John Wiley & Sons, Inc. 
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Library of Congress Cataloging in Publication Data: 
Billingsley, Patrick. 
Convergence of probability measures / Patrick Billingsley. - 2nd 
ed. 
p.  cm. - (Wiley series in probability and statistics. 
Probability and statistics) 
“Wiley-Interscience publication.” 
Includes bibliographical references and indexes. 
ISBN 0-471-19745-9 (alk. paper) 
1. Probability measures.  2. Metric spaces.  3. Convergence. 
I. Title.  11. Series: Wiley series in probability and statistics. 
Probability and statistics. 
QA273.6.BS5  1999 
5 1 9 . 2 4 ~ 2  1 
99-30372 
CIP 
Printed in the United States of America 
1 0 9 8 7 6  
PREFACE 
From  the preface  to the first  edition.  Asymptotic  distribution  theo- 
rems in  probability  and statistics have  from the beginning depended 
on  the classical theory  of  weak  convergence of  distribution  functions 
in  Euclidean  spat-onvergence, that  is, at  continuity  points  of  the 
limit  function.  The past  several decades have seen the creation  and 
extensive application  of  a  more inclusive theory  of  weak  convergence 
of  probability  measures on metric spaces. There are many asymptotic 
results that  can be  formulated within the classical theory but  require 
for their proofs this more general theory, which thus does not  merely 
study itself.  This book is about weak-convergence methods in metric 
spaces, with applications sufficient to show their power and utility. 
The second  edition.  A  person  who  read  the  first  edition  of  this 
book  when  it  appeared  thirty  years  ago  could  move  directly  on  to 
the periodical literature and to research in the subject.  Although the 
book  no  longer takes  the reader  to  the current  boundary  of  what  is 
known in this area of  probability  theory, I think it  is still useful as a 
textbook one can study before tackling the industrial-strength treatises 
now  available.  For  the  second  edition  I  have  reworked  most  of  the 
sections, clarifying some and shortening others (most notably the ones 
on dependent  random variables) by  using discoveries of  the last thirty 
years, and I have added some new topics.  I have written with students 
in mind; for example, instead  of  going directly to the space D [  0, oo), 
I have moved, in what I hope are easy stages, from C[O, I] to D[O, 11 
to D[O,oo).  In  an  earlier  book  of  mine,  I  said  that  I  had  tried  to 
follow  the excellent  example of  Hardy  and  Wright,  who  wrote  their 
Introduction  to the  Theory of  Numbers with the avowed aim, as they 
say in the preface, of  producing an interesting book, and I have again 
taken them as my  model. 
Chicago, 
January  1999 
Patrick  Billingsley 
V 
For  mathematical  information  and  advice, I  thank  Richard  Arratia, 
Peter  Donnelly, Walter Philipp, Simon Tavar6, and Michael Wichura. 
For  essential help on Tex  and the figures, I thank  Marty Billingsley 
and Mitzi Nakatsuka. 
PB 
CONTENTS 
Introduction 
Chapter 1. Weak  convergence in Metric Spaces 
Section 1.  Measures on Metric  Spaces, 7 
1 
7 
Measures and Integrals.  Tightness. Some Examples.  Problems. 
Section 2.  Properties of  Weak  Convergence, 14 
The  Portmanteau  Theorem.  Other  Criteria. 
Theorem.  Product  Spaces.  Problems. 
,The Mapping 
Section 3.  Convergence in Distribution, 24 
Random Elements.  Convergence in Distribution.  Convergence 
in Probability.  Local us. Integral Laws.  Integration  to the Limit. 
Relative measure.*  Three Lemmas.*  Problems. 
Section 4.  Long Cycles and Large Divisors,*  38 
Long  Cycles.  The Space  A.  The Poisson-Dirichlet  Distribu- 
tion.  Size-Biased Sampling.  Large  Prime  Divisors.  Technical 
Arguments.  Problems. 
Section 5 .  Prohorov’s Theorem, 57 
Relative  Compactness.  Tightness.  The Proof.  Problems. 
Section 6.  A  Miscellany,* 65 
The Ball  a-Field.  Slcorohod’s  Representation  Theorem.  The 
Prohorov  Metric.  A  Coupling Theorem.  Problems. 
Chapter 2.  The Space C 
Section 7 .  Weak Convergence and Tightness in C, 80 
* Starred topics can be omitted on a first reading 
80 
vii 
viii 
CONTENTS 
Tightness and  Compactness in C .  Random Functions.  Coordi- 
nate  Variables.  Problems. 
Section 8.  Wiener Measure and Donsker’s Theorem, 86 
Wiener Measure.  Construction of  Wiener Measure.  Donsker ’s 
Theorem.  A n  Application.  The Brownian Bridge.  Problems. 
Section 9.  Functions of  Brownian Motion Paths, 94 
Maximum and  Minimum.  The Arc  Sane  Law.  The Brownian 
Bridge.  Problems. 
Section 10. Maximal Inequalities,lO5 
Maxima of  Partial  Sums. A More  General  Inequality.  A Fur- 
ther Inequality.  Problems. 
Section 11. Trigonometric Series: 
113 
Lacunary  Series.  Incommensurabl e  Arguments.  Problem. 
Chapter 3.  The Space D 
Section 12. The Geometry of  D, 121 
121 
The Definition.  The Skorohod Topology. Separability and  Com- 
pleteness  of  D.  Compactness in D. A Second Characterization 
of  Compactness.  Finite-Dimensional  Sets.  Random Functions 
in D.  The Poisson Lamat.*  Problems. 
Section 13. Weak Convergence and Tightness in D, 138 
Finite-Dimensional  Distributions.  Tightness.  A  Criterion  for 
Convergence.  A  Criterion for Existence.“  Problem. 
Section 14. Applications, 146 
Donsker’s  Theorem Again.  A n  Extension.  Dominated  Mea- 
sures.  Empirical  Distribution  Functions.  Random Change  of 
Time. Renewal  Theory.  Problems. 
Section 15. Uniform Topologies,”  156 
The Uniform Metric  on D[ 0,1]. A  Theorem of  Dudley’s.  Em- 
pirical  Processes  Indexed  by Convex Sets. 
Section 16. The Space D[ 0, oo), 166 
Definitions.  Properties  of  the Metric.  SeparabilitQ  and  Com- 
pleteness.  Compactness.  Finite-Dimensional  Sets.  Weak Con- 
vergence.  Tightness. Aldous ’s Tightness Criterion.