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I have a large diagram of dependencies that I want to put in a math paper. I want some of the arrows to denote implication, and I want crossed-out arrows to denote specific non-implications. Here's a small part of it.

\xymatrix{
& \txt{Dedekind} \ar@2[dl] \ar@2[dr]|{\object@{/}}\\
\txt{Noetherian\\ normal} & & \txt{globally\\ perinormal}
}

The little portion of my chart above means that every Dedekind domain is Noetherian normal, but that there exist Dedekind domains that are not globally perinormal. However, the cross-out slash of the arrow, when done this way, is rather small. I'm worried that a casual reader would think the slash is a mistake, and that I actually mean that all Dedekind domains are globally perinormal.

How do I make the slash a lot bigger? Is this even possible with Xy-pic?

2

May I recommend to use for this?

% arara: pdflatex

\documentclass{article}
\usepackage[all,cmtip]{xy}
\usepackage{tikz-cd}
\usetikzlibrary{decorations.markings}
\tikzset{degil/.style={
        decoration={markings,
            mark= at position 0.5 with {
                \node[transform shape] (tempnode) {$\backslash$};}},
        postaction={decorate}}}
\newcommand{\textCDedge}[1]{\begin{tabular}{@{}c@{}}#1\end{tabular}} % you may switch to 'l' or alike later, if you do not like the centred alignment anymore

\begin{document}
\[  
\xymatrix{ & \txt{Dedekind} \ar@2[dl] \ar@2[dr]|{\object@{/}}\\ \txt{Noetherian\\ normal} & & \txt{globally\\ perinormal} }
\]  
\[
\begin{tikzcd}[arrows=Rightarrow]
& \textCDedge{Dedekind} \ar{dl} \ar[degil]{dr}&\\
\textCDedge{Noetherian \\ normal}&& \textCDedge{globally\\perinormal}
\end{tikzcd}
\]
\end{document}

enter image description here

The package is much more modern, powerful and easier to read. It would be easy to rewrite your existing diagram as the \ar can be used in both packages and you could redefine \txt to my definition of \textCDedge.

  • Thank you! And by the way, if I wanted to put labels above the arrows, how would I do that? – neil Dec 15 '14 at 16:59
  • @neil sorry, I am on a mobile. Please see any post tagged as tikz-cd or read the manual. It's really easy. – LaRiFaRi Dec 15 '14 at 17:54

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