# Centering vertically in table cell with other rotated cells

I would like to center the Available Expression, Very Busy Expression... Live Variables cells. The following code aligns the quoted cells only on the bottom of the cell itself: is there a way to center vertically even those cells? Thanks in advance.

\usepackage{bbm}
\usepackage[italian]{babel}
\usepackage[italian]{varioref}
\usepackage{rotating}
\usepackage{pgf,tikz}
\usepackage{etex}
\usepackage{tikz-cd}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[utf8]{inputenx}
\usepackage{braket}
\usepackage[a4paper]{geometry}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{mathabx}
\usepackage{examples}
\usepackage{multirow}
\newcolumntype{P}[1]{>{\centering\arraybackslash}p{#1}}
\newcolumntype{M}[1]{>{\centering\arraybackslash}m{#1}}

......

\begin{tabular}{c|M{20mm} M{30mm}}
& forward ($flow$) & backward ($flow^R$)\\
\midrule
\spheading[4em]{must ($\cap$)} & Available Expression & Very Busy Expression\\
\spheading[4em]{may ($\cap$)} & Reaching Definition & Live Variables\\
\bottomrule
\end{tabular}


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When you write $flow$, LaTeX typesets this as the quantities f, l, o and w all "multiplied together". You should use $\mathit{flow}$ and $\mathit{flow}^R$ instead. Also, one of your \caps should be a \cup. –  John Wickerson May 22 '13 at 14:42
It's better if you post a complete compilable .tex file, starting with \documentclass. Otherwise people trying to reproduce your problem have to guess which packages (e.g. booktabs) you've loaded. –  John Wickerson May 22 '13 at 14:55
Your're right. Thanks for the tip. –  jackb May 22 '13 at 14:56

You can get a reasonable approximation by putting \raisebox{-1.5em}{...} around your \rotatebox.

## Code

\documentclass{article}
\usepackage{array}
\usepackage{booktabs}
\usepackage{graphicx}

\raisebox{-1.5em}{\rotatebox{90}{\parbox{#1}{\raggedright #2}}}}
\newcolumntype{P}[1]{>{\centering\arraybackslash}p{#1}}
\newcolumntype{M}[1]{>{\centering\arraybackslash}m{#1}}

\begin{document}
\begin{tabular}{c|M{20mm} M{30mm}}
& forward ($\mathit{flow}$) & backward ($\mathit{flow}^R$)\\
\midrule
\spheading[4em]{must ($\cap$)} & Available Expression & Very Busy Expression\\
\spheading[4em]{may ($\cap$)} & Reaching Definition & Live Variables\\
\bottomrule
\end{tabular}
\end{document}


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