.NH
Photocomposition
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Photocomposition techniques
can be used to solve some of the problems of typesetting mathematics.
A phototypesetter is a device which exposes
a piece of photographic paper or film, placing characters
wherever they are wanted.
The Graphic Systems phototypesetter[2] on the
.UC UNIX
operating
system[3] works by shining light through a character stencil.
The character is made the right size by lenses,
and the light beam directed by fiber optics
to the desired place on a piece of photographic paper.
The exposed paper is developed and typically used
in some form of photo-offset reproduction.
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On
.UC UNIX ,
the phototypesetter is driven by a formatting program called
.UC TROFF
[4].
.UC TROFF
was designed for setting running text.
It also provides all of the facilities that one needs for
doing mathematics, such as
arbitrary horizontal and vertical motions,
line-drawing, size changing,
but the syntax for describing these special operations is
difficult to learn,
and difficult even for experienced users to type correctly.
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For this reason we decided to use
.UC TROFF
as an ``assembly language,''
by
designing a language for describing mathematical
expressions,
and compiling it into
.UC TROFF .
