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Commit 0d3c32ac authored by Luke Naylor's avatar Luke Naylor
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Correction Q->R plus Sebi wording suggestion

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...@@ -10,6 +10,7 @@ ...@@ -10,6 +10,7 @@
\newcommand{\QQ}{\mathbb{Q}} \newcommand{\QQ}{\mathbb{Q}}
\newcommand{\ZZ}{\mathbb{Z}} \newcommand{\ZZ}{\mathbb{Z}}
\newcommand{\RR}{\mathbb{R}}
\newcommand{\chern}{\operatorname{ch}} \newcommand{\chern}{\operatorname{ch}}
\newcommand{\lcm}{\operatorname{lcm}} \newcommand{\lcm}{\operatorname{lcm}}
\newcommand{\gcd}{\operatorname{gcd}} \newcommand{\gcd}{\operatorname{gcd}}
...@@ -28,12 +29,12 @@ Practical Methods for Finding Pseudowalls} ...@@ -28,12 +29,12 @@ Practical Methods for Finding Pseudowalls}
\section{Introduction} \section{Introduction}
[ref] shows that for any $\beta_0 \in \QQ$, [ref] shows that for any rational $\beta_0$,
the vertical line $\{\sigma_{\alpha,\beta_0} \colon \alpha \in \QQ_{>0}\}$ only the vertical line $\{\sigma_{\alpha,\beta_0} \colon \alpha \in \RR_{>0}\}$ only
intersects finitely many walls. A consequence of this is that if intersects finitely many walls. A consequence of this is that if
$\beta_{-} \in \QQ$, then there can only be finitely many circular walls to the $\beta_{-}$ is rational, then there can only be finitely many circular walls to the
left of the vertical wall $\beta = \mu$. left of the vertical wall $\beta = \mu$.
On the other hand, when $\beta_{-} \not\in \QQ$, [ref] showed that there are On the other hand, when $\beta_{-}$ is not rational, [ref] showed that there are
infinitely many walls. infinitely many walls.
This dichotomy does not only hold for real walls, realised by actual objects in This dichotomy does not only hold for real walls, realised by actual objects in
...@@ -43,11 +44,11 @@ which satisfy certain numerical conditions which would be satisfied by any real ...@@ -43,11 +44,11 @@ which satisfy certain numerical conditions which would be satisfied by any real
destabilizer, regardless of whether they are realised by actual elements of destabilizer, regardless of whether they are realised by actual elements of
$\bddderived(X)$. $\bddderived(X)$.
Since real walls are a subset of pseudowalls, the $\beta_{-} \not\in \QQ$ case Since real walls are a subset of pseudowalls, the irrational $\beta_{-}$ case
follows immediately from the corresponding case for real walls. follows immediately from the corresponding case for real walls.
However, the $\beta_{-} \in \QQ$ case involves showing that the following However, the rational $\beta_{-}$ case involves showing that the following
conditions only admit finitely many solutions (despite the fact that the same conditions only admit finitely many solutions (despite the fact that the same
conditions admit infinitely many solutions when $\beta_{-} \not\in \QQ$). conditions admit infinitely many solutions when $\beta_{-}$ is irrational).
For a destabilizing sequence For a destabilizing sequence
......
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