Download Geometry Of Surfaces B3 Course 2004 (Lecture notes) by Nigel Hitchin PDF

By Nigel Hitchin

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Discontinuous Groups of Isometries in the Hyperbolic Plane

This publication by means of Jakob Nielsen (1890-1959) and Werner Fenchel (1905-1988) has had
a lengthy and complex historical past. In 1938-39, Nielsen gave a sequence of lectures on
discontinuous teams of motions within the non-euclidean aircraft, and this led him - in the course of
World warfare II - to put in writing the 1st chapters of the e-book (in German). while Fenchel,
who needed to get away from Denmark to Sweden a result of German profession,
returned in 1945, Nielsen initiated a collaboration with him on what turned recognized
as the Fenchel-Nielsen manuscript. at the moment they have been either on the Technical
University in Copenhagen. the 1st draft of the Fenchel-Nielsen manuscript (now
in English) was once accomplished in 1948 and it used to be deliberate to be released within the Princeton
Mathematical sequence. notwithstanding, as a result of the speedy improvement of the topic, they felt
that giant adjustments needed to be made ahead of e-book.
When Nielsen moved to Copenhagen college in 1951 (where he stayed till
1955), he used to be a lot concerned with the foreign association UNESCO, and the
further writing of the manuscript was once left to Fenchel. The files of Fenchel now
deposited and catalogued on the division of arithmetic at Copenhagen Univer-
sity include unique manuscripts: a partial manuscript (manuscript zero) in Ger-
man containing Chapters I-II (

I -15), and an entire manuscript (manuscript I) in
English containing Chapters I-V (

1-27). The information additionally comprise a part of a corre-
spondence (first in German yet later in Danish) among Nielsen and Fenchel, the place
Nielsen makes particular reviews to Fenchel's writings of Chapters III-V. Fenchel,
who succeeded N. E. Nf/Jrlund at Copenhagen college in 1956 (and stayed there
until 1974), used to be a great deal concerned with a radical revision of the curriculum in al-
gebra and geometry, and targeted his examine within the concept of convexity, heading
the overseas Colloquium on Convexity in Copenhagen 1965. for nearly twenty years
he additionally positioned a lot attempt into his task as editor of the newly began magazine Mathematica
Scandinavica. a lot to his dissatisfaction, this task left him little time to complete the
Fenchel-Nielsen undertaking the best way he desired to.
After his retirement from the college, Fenchel - assisted by means of Christian Sieben-
eicher from Bielefeld and Mrs. Obershelp who typed the manuscript - chanced on time to
finish the publication effortless Geometry in Hyperbolic area, which used to be released by way of
Walter de Gruyter in 1989 almost immediately after his loss of life. concurrently, and with a similar
collaborators, he supervised a typewritten model of the manuscript (manuscript 2) on
discontinuous teams, elimination a few of the vague issues that have been within the unique
manuscript. Fenchel informed me that he pondered elimination components of the introductory
Chapter I within the manuscript, when you consider that this is able to be lined by means of the e-book pointed out above;
but to make the Fenchel-Nielsen publication self-contained he eventually selected to not do
so. He did choose to miss
27, entitled Thefundamental workforce.

As editor, i began in 1990, with the consent of the criminal heirs of Fenchel and
Nielsen, to provide a TEX-version from the newly typewritten model (manuscript 2).
I am thankful to Dita Andersen and Lise Fuldby-Olsen in my division for hav-
ing performed a superb activity of typing this manuscript in AMS- TEX. i've got additionally had
much support from my colleague J0rn B0rling Olsson (himself a pupil of Kate Fenchel
at Aarhus collage) with the evidence analyzing of the TEX-manuscript (manuscript three)
against manuscript 2 in addition to with a basic dialogue of the variation to the fashion
of TEX. In such a lot respects we determined to stick with Fenchel's intentions. besides the fact that, turning
the typewritten variation of the manuscript into TEX helped us to make sure that the notation,
and the spelling of yes key-words, will be uniform during the ebook. additionally,
we have indicated the start and finish of an evidence within the traditional type of TEX.
With this TEX -manuscript I approached Walter de Gruyter in Berlin in 1992, and
to my nice reduction and pride they agreed to put up the manuscript of their sequence
Studies in arithmetic. i'm such a lot thankful for this optimistic and quickly response. One
particular challenge with the ebook became out to be the copy of the various
figures that are a vital part of the presentation. Christian Siebeneicher had at
first agreed to bring those in ultimate digital shape, yet by way of 1997 it turned transparent that he
would now not have the ability to locate the time to take action. notwithstanding, the writer provided an answer
whereby I may still bring particular drawings of the figures (Fenchel didn't go away such
for Chapters IV and V), after which they might set up the creation of the figures in
electronic shape. i'm very thankful to Marcin Adamski, Warsaw, Poland, for his positive
collaboration about the genuine creation of the figures.
My colleague Bent Fuglede, who has personaHy identified either authors, has kindly
written a brief biography of the 2 of them and their mathematical achievements,
and which additionally locations the Fenchel-Nielsen manuscript in its right point of view. In
this connection i want to thank The Royal Danish Academy of Sciences and
Letters for permitting us to incorporate during this publication reproductions of photos of the 2
authors that are within the ownership of the Academy.
Since the manuscript makes use of a couple of particular symbols, a listing of notation with brief
explanations and connection with the particular definition within the ebook has been integrated. additionally,
a accomplished index has been extra. In either situations, all references are to sections,
not pages.
We thought of including an entire checklist of references, yet made up our minds opposed to it as a result of
the overwhelming variety of learn papers during this region. as a substitute, a miles shorter
list of monographs and different accomplished money owed appropriate to the topic has been
collected.
My ultimate and such a lot honest thank you visit Dr. Manfred Karbe from Walter de Gruyter
for his commitment and perseverance in bringing this ebook into lifestyles.

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Extra resources for Geometry Of Surfaces B3 Course 2004 (Lecture notes)

Sample text

Now from (4), λn · ru ∧rv = (nu ∧nv ) · (ru ∧rv ) = (nu · ru )(nv · rv ) − (nu · rv )(nv · ru ) = LN − M 2 62 but also n · ru ∧rv = which gives √ EG − F 2 √ λ = (LN − M 2 )/ EG − F 2 . (5) It follows that LN − M 2 and hence K depends only on the first fundamental form. 6 The Gauss-Bonnet theorem One of the beautiful features of the Gaussian curvature is that it can be used to determine the topology of a closed orientable surface – more precisely we can determine the Euler characteristic by integrating K over the surface.

If f vanishes at c then f (z) = (z − c)m (c0 + c1 (z − c) + . ) where c0 = 0. In particular zeros are isolated. • If f is non-constant it maps open sets to open sets. • |f | cannot attain a maximum at an interior point of a disc (“maximum modulus principle”). • f : C → C preserves angles between differentiable curves, both in magnitude and sense. 1 A Riemann surface is orientable. Proof: Assume X contains a M¨obius band, and take a smooth curve down the centre: γ : [0, 1] → X. In each small coordinate neighbourhood of a point on the curve ϕU γ is a curve in a disc in C, and rotating the tangent vector γ by 90◦ or −90◦ defines an upper and lower half: Identification on an overlapping neighbourhood is by a map which preserves angles, and in particular the sense – anticlockwise or clockwise – so the two upper halves agree on the overlap, and as we pass around the closed curve the strip is separated into two halves.

We now have a first fundamental form Edu2 + 2F dudv + Gdv 2 depending on t and we calculate 1∂ (Edu2 + 2F dudv + Gdv 2 )|t=0 = −(ru · nu du2 + (ru · nv + rv · nu )dudv + rv · nv dv 2 ). 2 ∂t The right hand side is the second fundamental form. From this point of view it is clearly the same type of object as the first fundamental form — a quadratic form on the tangent space. In fact it is useful to give a slightly different expression. Since n is orthogonal to ru and rv , 0 = (ru · n)u = ruu · n + ru · nu and similarly ruv · n + ru · nv = 0, rvu · n + rv · nu = 0 and since ruv = rvu we have ru · nv = rv · nu .

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