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Emeritus Professor Alfred Jacobus (Alf) van der Poorten
16 May 1942 { 9 October 2010

On 9th October 2010, at the young age of 68, Alf van der Poorten died frommetastatic lung cancer. He had been ill for two and a half years and endured
three operations and several rounds of radiotherapy and chemotherapy, but noneof these treatments was able to arrest the progress of his illness. Australia has lost
one of its leading pure mathematicians.
Alf was born in Amsterdam in 1942 and spent the war years as ‘Fritsje’, theyoungest child of the Teerink family in Amersfoort. His real parents, David andMarianne van der Poorten, were among the few who returned from the camps. Alf
was reunited with them in 1945. His family, including sisters Malieke and Rose,migrated to Sydney aboard the SS Himalaya in early 1951. Eventually the family
settled in Bellevue Hill where David van der Poorten became a successful generalpractitioner.
Alf modestly claimed to have ‘survived the ministrations of Sydney Boys HighSchool’. In fact he excelled, and was ranked among the top few students in New
South Wales in the Leaving Certificate Examination. After a year in a youth
leadership program in Israel, Alf accepted a cadetship in mathematics at theUniversity of New South Wales (UNSW) in 1961.
Alf was a student and then an academic at UNSW for eighteen years. Altogether
he collected four degrees from the university. He first graduated in 1965 from aBachelor of Science degree with Honours in Pure Mathematics. He next completed
his doctorate in 1968. Alf avoided the compulsory general studies subjects of thescience degree by pursuing a concurrent major sequence in Philosophy, which helater converted to a Bachelor of Arts with Honours. Lest his education be totally
impractical, he then proceeded to complete an MBA degree.

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Obituary: Emeritus Professor Alfred Jacobus (Alf) van der Poorten

During the 1960s Alf was extremely active politically. He was President of theUNSW Students’ Union Council from 1964 to 1965 and President of the UNSW
University Union from 1965 to 1967. He served on the Council of the University
from 1967 to 1973. He was also National President of the Jewish youth movement
Betar, President of the Australian Union of Jewish Students and President of theState Zionist Youth Council. In 1966 he received the Australian Youth CitizenshipAward ‘for his attainments in community service, academic achievement andyouth leadership’. Alf joined the Board of Directors of the University Co-operative
Bookshop Ltd in 1965 and remained a Director until 1982, serving as Chairmanof the Board from 1979.
Alf was interested in all of mathematics but his research was in diverse aspects ofnumber theory. His doctoral supervisor was Kurt Mahler, who was a Professorial
Fellow in the Research School of Mathematical Sciences at the Australian National
University. Alf’s thesis was entitled ‘Simultaneous algebraic approximations tofunctions’ and it was in this work that he made his first contributions totranscendence theory. It is no surprise that Alf’s second paper was a note on‘Transcendental entire functions mapping every algebraic number field into itself’.
At UNSW he was particularly influenced by his teachers John Blatt and GeorgeSzekeres.
Alf was appointed Lecturer in Pure Mathematics at UNSW in 1969. I first met
him late in 1970, at the time of my appointment, and he was already de facto Headof Department since George Szekeres had no interest in administrative details. Alfwas promoted to Senior Lecturer in 1972 and to Associate Professor in 1976.
In 1972 John Loxton joined the department, and over the next decade Alf andJohn wrote twenty-one joint research papers — all of them serious contributions tonumber theory. A number of these papers were contributions to Baker’s method of
linear forms in the logarithms of algebraic numbers and some extended Mahler’s
method for determining transcendence and algebraic independence. Other papers
related to growth of recurrence sequences and algebraic functions satisfying
functional equations, and there was a sequence of papers investigating arithmeticproperties of certain functions in several variables. They also wrote about regularsequences and automata. The collaboration of Alf van der Poorten and JohnLoxton was clearly the most important of both their mathematical careers.
During the 1970s Alf spent time on study leave in Leiden, Cambridge (UK) andKingston (Ontario). His hosts were Robert Tijdeman, Alan Baker and Paulo
Ribenboim. He took advantage of this time outside Australia to rapidly build
his network of mathematical collaborators. Later sabbatical leave periods took
Alf, and often his whole family, to Israel, Bordeaux, Delft, Helsinki and Princeton.
In 1979, Alf was appointed Professor of Mathematics at Macquarie University.
He was immediately immersed in administrative duties but still found the timeand energy to expand his research output. He served as Head of the School ofMathematics, Physics, Computing and Electronics from 1980 to 1987 and again
from 1991 to 1996. Macquarie University was founded only in the 1960s. Alf wasasked to increase the research profile of the School, and he succeeded in thisthrough making a number of excellent appointments.

Obituary: Emeritus Professor Alfred Jacobus (Alf) van der Poorten

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In the periods he was not Head of School, Alf served on the Academic Senate.
As Presiding Member of the Academic Senate he was a member of Macquarie
University’s Senior Executive and an ex-officio member of the University Council
until his retirement from administrative activity at the end of 2001. Alf retired
from Macquarie in 2002.
An unusual aspect of Alf’s research output was the number of his joint authors.
Of his publications, 178 have been reviewed by Maths Reviews, and this number
will rise over the next couple of years. Once he moved to Macquarie University
both Alf’s scholarship and his research output rapidly increased with a constantstream of overseas visitors, mainly courtesy of the Australian Research Council.
MathSciNet currently lists sixty-five of Alf’s co-authors, with the most frequentcollaborators being John Loxton, Michel Mendès France and Hugh Williams. The
list also includes Enrico Bombieri, Richard Brent, John Coates, Paula Cohen,
Bernhard Dwork, K. Inkeri, Sidney Morris, Bernhard Neumann, Jeffery Shallit,
Igor Shparlinski, Robert Tijdeman and Michel Waldschmidt.
In a document such as this it is not possible to fully analyse Alf’s research output.
Perhaps it is best to mention work that Alf believed to be highlights of his research.
He certainly considered much of the work with Loxton to be important.
In addition, in 1988 he solved Pisot’s conjecture on the Hadamard quotient of two
rational functions and he used these ideas to produce a new proof of the celebrated
S-unit theorem. In 1992, jointly with Bernie Dwork, he studied the ‘Eisensteinconstant’, providing sharp bounds on the Taylor coefficients of an algebraic powerseries. Work begun in the early 1980s with Bombieri led to the invariant Thue–Siegel method being applied to the explicit construction of curves with prescribedsingularities. Finally, in 1999, Alf and Kenneth Williams succeeded in breaking up
the Chowla–Selberg formula, allowing evaluation of the Dedekind eta function for
all discriminants in terms of singular values of the L-functions.
Alf always attempted to prove that ‘mathematics is beautiful, elegant and fun,a language as worthwhile learning as any other’, as he remarked to a reporterin 1979. In part this was done by giving vivid and interesting colloquium talks
on five continents. In addition, he put real effort into expository writing. One
example of this was in 1978 when ‘A proof that Euler missed . . . Apéry’s proofof the irrationality of ζ(3)’ appeared in the first volume of the MathematicalIntelligencer. Apéry was a professor of chemistry whose seminar on this surprising
result was very terse and not believed by some mathematicians in the audience.
Alf sorted out the details and published a full proof. I heard him give a very
successful seminar on this material at Rutgers University in 1978. This talk wasgiven at a dozen departments in the US during the fall of that year. As a second
example, his fine book ‘Notes on Fermat’s Last Theorem’ was published by WileyInterscience in 1996. Alf claimed that reading it ‘required little more than one yearof university mathematics and an interest in formulas’. This is not quite true but
nevertheless the book was awarded an American Publishers’ Award for Excellencein Mathematics.
Alf made significant contributions to the mathematics profession both within
Australia and overseas. He was the founding Editor of the Australian MathematicalSociety Gazette, served on the Council of the Society for many years and was36

Obituary: Emeritus Professor Alfred Jacobus (Alf) van der Poorten

President from 1996 to 1998. As President, he worked hard to reduce any remaining
tension between pure and applied mathematicians in Australia. During his tenure
as president the Council agreed to underwrite the 5th International Congress on
Industrial and Applied Mathematics, ICIAM 2003, the first large mathematics
congress to be held in Australia. This was an important and visionary undertakingfor the Society.
In 1994–1995, Alf chaired a Working Party, with Noel Barton as Executive Officer,
on behalf of the National Committee for Mathematics to report on ‘Mathematical
Sciences Research and Advanced Mathematical Services in Australia’. In 1998 hewas a member of the Canadian National Science and Engineering Research Council(NSERC) site visit committee to evaluate Canada’s three national Mathematical
Sciences Research Institutes; and in 2003 he was a member of the Association ofUniversities in the Netherlands (VSNU) review committee for academic researchin mathematics. In 1998, Alf joined the new Committee on Electronic Information
Communication (CEIC) of the International Mathematical Union (IMU), and wasreappointed in 2002 and 2006; he was also one of Australia’s three delegates tothe quadrennial Assembly of the IMU at Dresden (1998), at Beijing (2002), andat Santiago de Compostela (2006).
Alf’s contribution to mathematics was recognised by the award of a Doctorate
Honoris Causa by the Université Bordeaux I in 1998, for which he was nominatedby Michel Mendès France. In his acceptance speech Alf noted that he had visitedthe department so many times that he considered it to be his third University.
In recognition of both his own mathematics and his services to mathematics inAustralia, Alf, jointly with Ian Sloan, was awarded the inaugural George Szekeres
Medal of the Australian Mathematical Society in 2002. He was also appointed a
Member of the Order of Australia (AM) in the Australia Day Honours List 2004,
for ‘service to mathematical research and education, particularly in the field ofnumber theory’.
Away from mathematics most of Alf’s interests were rather sedentary. His writingof mathematics seemed to occur during the ad-breaks in televised football. He
watched all the main codes of football as well as cricket, baseball and netball.
Above all, he supported the St George Rugby League Football team from theearly 1950s onwards. When mathematical inspiration was hard to come by heread science fiction and mysteries. Alf claimed never to have thrown a book away
and he thus owned some five thousand science fiction books and several thousand
mysteries; but he was ‘not a collector, just a keeper’. Since he also owned a coupleof thousand mathematics books almost no part of his family home was withoutbookshelves.
Alf is survived by his mother Marianne, his wife Joy, his children David and Kate,and four grandchildren Elizabeth, James, Gabrielle and Ellie.
On behalf of the mathematical community across Australia I acknowledge ourgreat respect for Alf’s achievements. We honour the very substantial contribution
Alf van der Poorten has made to mathematics in Australia.
David Hunt, University of New South Wales
E-mail: d.hunt@unsw.edu.au