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\subsection*{{\sc Prosper:} \LaTeX-based computer presentations}
 In many branches of science and engineering,  presentation
software, usually Microsoft's Powerpoint, has become a popular
tool for the delivery of research talks. Increasingly, 
such software is also being used in teaching. If used properly, 
presentation software combines the
advantages of traditional `chalk \& talk'--based teaching (arguments
can be developed step-by-step; sections of text can be erased while
others are kept `on the blackboard') with the benefits of 
computer-generated OHP slides, ensuring an attractive appearance 
regardless of one's handwriting. It also adds the ability to incorporate 
computer-generated graphics and animations.

 Recently, Fr\'{e}d\'{e}ric Goulard has developed a new document class
that allows the creation of computer-based presentations
in \LaTeX: {\sc Prosper}, based on the {\tt seminar} class, 
originally written by Timothy Van Zandt. The class, documentation and
many examples may be downloaded from the prosper home page 
{\tt \small http://prosper.sourceforge.net}. A number of style
files are provided, defining generic templates
for each slide: e.g. colours, fonts, logos, etc., which can easily be
modified to suit individual needs.

 After processing the \LaTeX\ source, the dvi file may be used to
 generate two different output formats:
  \textsl{Portable Document Format} (PDF) for displaying the slides
  on-screen; or \textsl{Postscript} for printing backup transparencies.
 Postscript files are produced in the normal manner using {\tt dvips}
 and the PDF files are, in fact, derived from the Postscript using 
 {\tt ps2pdf}, available with recent GhostScript  distributions. {\sc
 Prosper} does not yet support {\tt pdflatex}, so direct conversion to
 PDF from the source is not possible.

PDF is a highly portable format and may be displayed on a wide variety
of hardware platforms with the Acrobat\Registered reader 
(available for free download from  
{\tt\small http://www.adobe.com/products/acrobat}). Acroread includes
a full-screen mode for presentations $<$Ctrl l$>$ and supports a
number of different transition effects between slides (replace,
dissolve, glitter,...) that may be defined in the \LaTeX\ source.

 A key feature of the prosper class is the use of overlays to control 
the appearance of certain sections of text on the screen, 
illustrated in the following example:
{\small
\begin{verbatim} 
\overlays{3}{
\begin{slide}{Title of the slide}
This text is visible throughout. 
\untilSlide{2}{This text appears until slide two.}
\fromSlide{2}{This text appears from slide two.}
\onlySlide{3}{This text only appears on slide three.}
\end{slide}}
\end{verbatim} 
In the above, the text specified in the arguments 
remains displayed at its original position even if the space `above'
it becomes available subsequently. The starred versions of
the three commands (e.g. {\tt $\backslash$fromSlide*\{n\}\{\}}) reformats 
the page to fill any gaps that appear when material is removed and
should be used for replacement purposes.

External graphics may be included with standard \LaTeX\ packages such
as {\tt epsfig} and {\tt graphics}; and the {\tt pstricks} package
can be used to produce lively annotations and effects, see the file {\tt
prosper-tour.tex} included in the distribution. 
The {\sc Prosper} class includes the {\tt hyperref.sty} package by 
Sebastian Rahtz, which may be used to define internal and external
hyperlinks within the document. In particular, hyperlinks to external 
animations may be created via the command
\begin{verbatim} 
\href{run:WonderfulAnimation.avi}{Start animation} 
\end{verbatim}
\noindent
 The hyperlink ``Start animation'' spawns a multimedia player, 
defined by Acroread, that displays the movie WonderfulAnimation.avi in
a new window. In this example, WonderfulAnimation.avi must be in the
same directory as the pdf file, although, of course, relative file
names may be specified. Direct links to Acroread menu options 
may also be created e.~g.
\begin{verbatim}
\Acrobatmenu{NextPage}{Next} \Acrobatmenu{PrevPage}{Prev}
\end{verbatim}
 defining two hyperlinks, Next and Prev, to the next and
 previous pages, respectively. Including such links in the generic
 style file allows the use of wireless mice to control presentations.

Two examples, illustrating the on-screen manipulation of fairly 
complex equations and the use of associated graphics can be found at \newline
\mbox{\tt \small http://www.maths.man.ac.uk/\ \hspace{-1.5mm}$\tilde{\,}$\hspace{0.5mm}mheil/Prosper}. 

  When we first used {\sc Prosper}, we were amazed how easy it was to convert 
existing \LaTeX-generated slides into electronic presentations. We
have now used {\sc Prosper} for many research presentations and
occasionally for teaching. The following points
might be useful for newcomers to computer-based presentations:
\begin{itemize}
\item LCD projectors are now widely available at conferences 
and incompatibilities between laptops and the projectors
tend to be rare(r). Nevertheless, we still prepare `backup' 
OHP slides in case of any hardware problems.

\item One drawback of any computer-based presentation is that
it is impossible to see the next slide before it appears on the screen.
To ensure a smooth talk, it is vital to remember the sequence of 
one's slides well. We (and a few other speakers whose talks we have
attended) have occasionally been surprised by the appearance of 
an `unexpected' slide.

\item Many speakers use Post-It notes to attach brief notes to their
OHP transparencies. We tend to use the {\tt $\backslash$onlyslide\{\}} 
command to briefly display any such notes (in a smaller fontsize) 
on the screen. 

\item It is very easy to customise the style files to include 
logos, frames and colourful backgrounds. However, it is important to 
remember that graphics can be distracting and that some 
backgrounds strongly reduce the readability of the text.
For maximum contrast, we prefer black text on a white background and 
tend to use colour only to highlight important sections 
of the text and the equations. 


\end{itemize}
To summarise, we feel that  Fr\'{e}d\'{e}ric Goulard has created an 
extremely useful tool which we expect to be
become very popular within the mathematical community. 

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Matthias Heil (M.Heil@maths.man.ac.uk) is a Lecturer and Andrew
L. Hazel (ahazel@maths.man.ac.uk) is a Postdoctoral Researcher in the 
Department  of Mathematics at the University of Manchester, UK.


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