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@ -27,3 +27,6 @@ Albanese
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Hirzebruch
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Hirzebruch
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multiplicitity
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multiplicitity
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subvariety
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subvariety
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Cremona
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equivariant
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bimeromorphic
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@ -36,7 +36,7 @@
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\todo{define torus quotient}
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\todo{define torus quotient}
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\begin{defn}[The $\cC$-Albanese of a compact pair with trivial boundary]\label{def:1-2}%
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\begin{defn}[\protect{The Albanese of a compact pair with trivial boundary, \cite[Def.~9.1]{orbiAlb2}}]\label{def:1-2}%
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Let $X$ be a compact Kähler manifold. An Albanese of the $\cC$-pair $(X,0)$
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Let $X$ be a compact Kähler manifold. An Albanese of the $\cC$-pair $(X,0)$
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is a torus quotient $(A, Δ_A)$ and a $\cC$-morphism
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is a torus quotient $(A, Δ_A)$ and a $\cC$-morphism
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\[
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\[
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@ -61,9 +61,9 @@
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\]
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\]
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\end{rem}
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\end{rem}
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\begin{thm}[The Albanese of a $\cC$-pair]\label{thm:22-1} %
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\begin{thm}[\protect{Existence of the Albanese, \cite[Thm.~9.2]{orbiAlb2}}]\label{thm:22-1} %
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Let $X$ be a compact Kähler manifold. If $q^+_{\Alb}(X,0) < ∞$, then an
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Let $X$ be a compact Kähler manifold. If $q^+_{\Alb}(X,0) < ∞$, then an
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Albanese of $(X,0)$ exists.
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Albanese of $(X,0)$ exists. \qed
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\end{thm}
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\end{thm}
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@ -26,12 +26,9 @@
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\bP¹ \ar[r, "n\text{, normalization}"'] \ar[rr, bend left=15, "\eta"] & C \ar[r, "\text{inclusion}"'] & X.
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\bP¹ \ar[r, "n\text{, normalization}"'] \ar[rr, bend left=15, "\eta"] & C \ar[r, "\text{inclusion}"'] & X.
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\end{tikzcd}
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\end{tikzcd}
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\]
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\]
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Consider the points $0 \in \bP¹$ and $x' := n(0) \in X$.
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Given that $X$ is smooth, recall from \cite[Ex.~8.6]{orbiAlb1} that $\eta$ is
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a $\cC$-morphism, between $\cC$-pairs $(\bP¹, 0)$ and $(X, 0)$. Since
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Given that $X$ is smooth, recall from \cite{orbiAlb1} that $\eta$ is a
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$\Alb(\bP¹,0)$ exists, the universal property of the Albanese yields a diagram
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$\cC$-morphism, between $\cC$-pairs $(\bP¹, 0)$ and $(X, 0)$. Since
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$\Alb(\bP¹,0)$ exists, the universal property of the Albanese yields a
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diagram
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\[
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\[
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\begin{tikzcd}[column sep=2cm]
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\begin{tikzcd}[column sep=2cm]
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\bP¹ \ar[r, "\alb(\bP¹{,}0)"] \ar[d, "n"'] & \Alb(\bP¹,0) \ar[d] \\
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\bP¹ \ar[r, "\alb(\bP¹{,}0)"] \ar[d, "n"'] & \Alb(\bP¹,0) \ar[d] \\
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@ -41,15 +38,18 @@
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The claim follows immediately once we observe that $\Alb(\bP¹,0)$ is a point.
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The claim follows immediately once we observe that $\Alb(\bP¹,0)$ is a point.
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\end{proof}
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\end{proof}
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\todo{There is nothing special about $\bP¹$ here. This works for every space with nontrivial $\cC$-Albanese.}
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\begin{cor}\label{cor:2}%
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\begin{cor}\label{cor:2}%
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In Setting~\ref{set:1}, let $\mu : X \to Y$ be a morphism to a normal
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In Setting~\ref{set:1}, let $\mu : X \to Y$ be a morphism to a normal analytic
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projective variety. If all fibres of $\mu$ are rationally chain connected,
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variety. If all fibres of $\mu$ are rationally chain connected, then
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then $\alb(X,0)$ factors via $\mu$,
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$\alb(X,0)$ factors via $\mu$,
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\[
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\[
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\begin{tikzcd}
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\begin{tikzcd}
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X \ar[r, "\mu"'] \ar[rr, bend left=15, "\alb(X{,}0)"] & Y \ar[r, "\exists!\:\beta"'] & \Alb(X,0).
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X \ar[r, "\mu"'] \ar[rr, bend left=15, "\alb(X{,}0)"] & Y \ar[r, "\exists!\:\beta"'] & \Alb(X,0).
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\end{tikzcd}
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\end{tikzcd}
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\]
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\]
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\qed
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\end{cor}
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\end{cor}
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\begin{cor}\label{cor:3}%
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\begin{cor}\label{cor:3}%
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@ -57,13 +57,52 @@
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$\Alb(X,0)$ is a point.
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$\Alb(X,0)$ is a point.
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\end{cor}
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\end{cor}
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\begin{cor}\label{cor:4}%
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In Setting~\ref{set:1}, let $\mu : X \to Y$ be a bimeromorphic modification of
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a compact manifold $Y$. Then, $\alb(X,0)$ factors via $\mu$,
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\[
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\begin{tikzcd}
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X \ar[r, "\mu"'] \ar[rr, bend left=15, "\alb(X{,}0)"] & Y \ar[r, "\exists!\:\beta"'] & \Alb(X,0),
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\end{tikzcd}
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\]
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the morphism $\beta$ is a $\cC$-morphism between the pairs $(Y,0)$ and
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$\Alb(X,0)$, and $\beta : (Y,0) \to \Alb(Y,0)$ is an Albanese of $(Y,0)$.
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\end{cor}
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\begin{proof}
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\todo{PENDING}
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\end{proof}
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\begin{cor}\label{cor:5}%
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In Setting~\ref{set:1}, let $Y$ be a compact Kähler manifold bimeromorphic to
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$X$. Then, an Albanese of $(Y,0)$ exists. If $f : X \dasharrow Y$ is
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bimeromorphic, then there exists a unique morphism of $\cC$-pairs rendering
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the following diagram commutative,
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\[
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\begin{tikzcd}
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X \ar[d, "\alb(X{,}0)"'] \ar[r, dashed, "f"] & Y \ar[d, "\alb(Y{,}0)"'] \\
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\Alb(X,0) \ar[r, "\exists! \alb(f)"'] & \Alb(Y,0)
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\end{tikzcd}
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\]
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\end{cor}
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\begin{proof}
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\todo{PENDING}
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\end{proof}
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\begin{cor}\label{cor:6}%
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In Setting~\ref{set:1}, the automorphism group of $X$ and the Cremona group
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act on $\Alb(X,0)$ in a way that makes the morphism $\alb(X,0)$ equivariant.
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\end{cor}
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\begin{proof}
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\todo{PENDING}
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\end{proof}
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\todo{
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\todo{
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\begin{itemize}
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\begin{itemize}
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\item Need example where a rational variety has a
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\item Factorization via minimal model.
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\item Factorization via minimal model.
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\item Independence of bimeromorphic model.
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\item For varieties of general type, factorization via the canonical.
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\item Factorization via MRC quotient.
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\end{itemize}
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\end{itemize}
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}
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}
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\begin{example}[Theorem~\ref{thm:1} is wrong for singular spaces]
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\begin{example}[Theorem~\ref{thm:1} is wrong for singular spaces]
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