Moving a subscript in Xy-pic

Question

To obtain a larger version of \nrightarrow (LaTeX, Package amssymb), I typed

$\xymatrix{A\ar@<-1.5ex>@{}[r]^{/}\ar[r]&B}$ 

Is there a simpler way to obtain the same result, i.e. is it possible to move upward or downward the subscript (or the superscript) of an arrow?

Answer 1

Really easy negation can be done with centernot:

% arara: pdflatex

\documentclass{article}
\usepackage{centernot}

\begin{document}
$\rightarrow\centernot\rightarrow\longrightarrow\centernot\longrightarrow\Rightarrow\centernot\Rightarrow\Longrightarrow\centernot\Longrightarrow$
\end{document}

You could negate anything with that. If you want to use a commutative diagram approach, take a look on tikz-cd. If you want to have the amssymb arrow, you will have to scale this up or do a feature request to the maintainers.