[Xy-pic] Spacing problems with triangles

[Jürgen Koslowski]

Hello,

I encountered an annoying spacing problem when displaying triangular
diagrams.  The top corner is much too close to the preceeding text, in
case of a short line even protrudes into that line.  So far I have
used invisible entries to get around this problem, is there a better
way?  Enclosing the diagram into \vcenter{...} does not help.

Here is an example:

\documentclass[11pt]{article}
\usepackage[arrow,2cell,line,dvips,ps]{xy}

%\CompileMatrices
\UseAllTwocells

\setlength{\textwidth}{16 cm}
\begin{document}

  If for a 2-cell
\[
\xy 
  ;<50 pt,0 pt>:
  (0.0,0)              *+{A}="A",
  (0.5,\halfrootthree) *+{B}="B",
  (1.0,0)              *+{C}="C",
  "A";"C",{\twocell<\omit>{<-3>{\ \phi}}},
  \ar_{t}"A";"C"
  \ar^{r}"A";"B"
  \ar^{s}"B";"C"
\endxy
\]
  pasting at $s$ is bijective, we call $\langle s,\phi\rangle$ a right
  extension of $t$ along $r$.

  Even if the line preceeding the diagram is longer, the placement
  is better but we still have a problem.  There seems to be too little
  space above the diagram:
\[
\xy 
  ;<50 pt,0 pt>:
  (0.0,0)              *+{A}="A",
  (0.5,\halfrootthree) *+{B}="B",
  (1.0,0)              *+{C}="C",
  "A";"C",{\twocell<\omit>{<-3>{\ \phi}}},
  \ar_{t}"A";"C"
  \ar^{r}"A";"B"
  \ar^{s}"B";"C"
\endxy
\]
  I don't want to put in extra invisible elements to get the spacing right.

\end{document}

-- 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 at iti.cs.tu-bs.de               and don't be late!
http://www.iti.cs.tu-bs.de/~koslowj      Jimi Hendrix (Voodoo Child, SR)