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Complex geometry is the study of complex manifolds, complex algebraic varieties, complex analytic spaces, and, by extension, of almost complex structures. It is a part of differential geometry, algebraic geometry and analytic geometry.

2 votes
0 answers
183 views

Zariski Connectedness Theorem in Complex Geometry

Let $f: X \to Y$ be a proper surjective morphism of complex irreducible varieties such that general fibre of $f$ is connected and $Y$ integrally closed\normal. Say, we even assume wlog $Y=\text{Spec}( …
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2 votes
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156 views

Construct Torsion element in $H^2(X,\mathbb{Z})$ with Ambrose–Singer theorem

Let $X$ be a Kahler manifold. Using the exponential sequence one obtains a homomorphism $c_1:H^1(X,\mathcal{O}_X^*)\rightarrow H^2(X,\mathbb{Z})$. This is associating to a holomorphic line bundle $L$ …
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2 votes
0 answers
83 views

Holomorphic map proper after shrinking (Kollar's Lecture on Resolution of Singularities)

I'm reading Janos Kolloar's Lecture on Resolution of Singularities and have some problems to understand a detail in the proof of Thm. 1.5 on page 10: Thm 1.5 (Riemann) Let $F(x,y)$ be an irreducibl …
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1 vote
0 answers
106 views

Isomorphic Jacobians for different choices of basis of $1$-forms

In Otto Forster's Lectures on Riemann Surfaces on page 170 Jacobi Variety is defined in 21.6: Suppose $X$ is a compact Riemann surface of genus $g$ and $ \omega_1,..., \omega_g $ is a basis of $\Omega …
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3 votes
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346 views

When are two complex Tori biholomorphic

Let $g \ge 1$ be a natural number and $\mathbb{C}^g$ complex vector space which is isomorphic to $\mathbb{R}^{2g}$ is real vector space. An additive subgroup $\Gamma \subset \mathbb{C}^g$ is called a …
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0 votes
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290 views

Chow's Lemma: Mumford's and Grothendieck's (?) definitions

David Mumford gives in his book Algebraic Geometry I, Complex Projective Varieties on page 61 a definition of Chow's Lemma which has at least for me not a usual form: If says that a closed $^*$-analyt …
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2 votes
1 answer
350 views

Comparison of classical and Zariski topologies with constructible sets

In David Mumford's book Algebraic Geometry I, Complex Projective Varieties the proof of (3.25) Specialization principle on page 53 contains an argument I not understand. General assumptions: all our v …
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1 vote
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693 views

Questions on Néron–Severi group

$\DeclareMathOperator\NS{NS}\DeclareMathOperator\Pic{Pic}$I have two questions on a comment from Daniel Hyubrechts's Complex Geometry on pages 133/134. Let $X$ be a compact Kähler manifold. Consider …
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2 votes
1 answer
133 views

Generically finite projection $\pi_L: X \to \mathbb{P}^2$ from plane $L$ and critical points

(In following we are working in "classical" complex setting: i.e. all involved schemes are considered to be varieties over $k=\mathbb{C}$) Let $X \subset \mathbb{P}^n$ be irreducible surface and $L $ …
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2 votes
1 answer
594 views

Example motivating mixed Hodge structures

The suggested intuition behind mixed Hodge structures - developed in particular to generalize Hodge decomposition of cohomology groups from complex smooth complete varieties to more general algebraic …
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1 answer
322 views

Self-intersection of zero section of line bundle over elliptic base curve

Let $C$ be an elliptic curve over $k=\mathbb{C}$ and $\mathcal{L}$ a line bundle of degree $d$. It induces naturally a $\mathbb{A}^1$-fibration $L \to C$ where $L=\underline{\operatorname{Spec}} (\ope …
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1 answer
278 views

Question about Correspondences from Mumford’s Complex Projective Varieties

I study David Mumford's Algebraic Geometry I - Complex Projective Varieties and have some problems to understand a step in the proof of Lemma 6.7 (b). Firstly, the general setting & preparations arou …
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201 views

Expansion around a singular point of a multivalued meromorphic function (due to Riemann/Cauchy)

In Riemann's publication about Abelian functions 'Theorie der Abelschen Functionen' (Here the original paper in german) at the end of Chapter 4, part 2 is clamed that for every Riemann surface $T$ and …
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3 votes
0 answers
220 views

Historical proof of Leschetz Hyperplane Theorem

I browse in Phillip Griffiths' Slides on historical development of Hodge-theory and these include a sketch of the original approach with Lefschetz used to study complex surfaces in his famous hypersur …
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2 votes
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1k views

Explicit construction of Fubini Study Metric

I have a question about a remark on Fubini Study metric on $\mathbb{CP}^n$ from Notes on canonical Kähler metrics on page 8 is remarked (Example 2.12 4.): Fix a Hermitian innerproduct on $\mathbb{C}^ …
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