[Xy-pic] pullback symbols

[Jürgen Koslowski]

Hello,

Looking back at Andrej Bauer's message from 30 Jul 2001, I decided to
upgrade my own pullback symbols for matrix environments, which were
rather clumsy.  The following version allows you to specify any angle
relative to the object where the decoration is desired (potentially
useful, if your diagram is not rectangular).

\newdir{pb}{:(1,-1)@^{|-}}
\def\pb#1{\save[]+<12 pt,0 pt>:a(#1)\ar@{pb{}}[]\restore}

You can adjust the distance from the object by changing the dimension
"12 pt" in the definition.  Here's a (nonsensical) example:

$$
\xymatrix{
  A\pb{315}
		\ar@{-}[rr] 
		\ar@{-}[d]  
&&B\pb{225} 
		\ar@{-}[d] 
		\cr
  C\pb{45}
		\ar@{-}[rr]
&&D\pb{135}
}
$$

-- Juergen

-- 
Juergen Koslowski               If I don't see you no more on this world
ITI, TU Braunschweig               I'll meet you on the next one
koslowj@iti.cs.tu-bs.de               and don't be late!
http://www.iti.cs.tu-bs.de/~koslowj      Jimi Hendrix (Voodoo Child, SR)