# How to cut a horizontal line by a perpendicular line?

I'd like to cut the line AC at the point p by a perpendicular line.

\documentclass{article}
\usepackage{xypic}
\begin{document}
\xymatrix{
& B\ar @{-}[d] &\\
A\ar @{-}[rr]_{P} &  & C
}
\end{document}

-
@MdKutubuddinSardar: Why don't you react to any of the comments? –  Jake Mar 22 '13 at 14:24
Please, at least have the decency to upvote and accept answers to your questions. –  Jake Mar 22 '13 at 14:30

To extend the vertical line down to the line AC, use the arrow adjustment facility placing +0{} after the arrow. By default the arrow stops short of the center of the node, this adjustment makes it stop distance 0 from the center instead.

\documentclass{article}

\usepackage{xypic}

\begin{document}
\xymatrix{
& B\ar @{-}[d]+0{} &\\
A\ar @{-}[rr]_{P} &  & C
}