.NHIntroduction.tr ^..PP.UL troff[1]is a text-formatting program,written by J. F. Ossanna,for producinghigh-quality printed output from the phototypesetteron the.UC UNIXand.UC GCOSoperating systems.This document is an example of.UL troffoutput..PPThe single most important ruleof using.UL troffisnot to use it directly, but through some intermediary.In many ways,.UL troffresembles an assembly language _a remarkably powerful and flexible one _but nonetheless such that many operations must be specifiedat a level of detail and in a form that is too hard for most people to use effectively..PPFor two special applications, there are programs that providean interface to.UL trofffor the majority of users..UL eqn [2]provides an easy to learn language for typesetting mathematics;the .UL eqnuserneed know no .UL troffwhatsoeverto typeset mathematics..UL tbl[3]provides the same convenience for producing tables of arbitrarycomplexity..PPFor producing straight text (which may well contain mathematics or tables), there are a number of `macro packages'that define formatting rules and operations for specific stylesof documents,and reduce the amount ofdirect contact with .UL troff .In particular, the `\-ms'[4]and PWB/MM [5]packagesfor Bell Labs internal memoranda and external papersprovide most of the facilities neededfor a wide range of document preparation.(This memo was prepared with `\-ms'.)There are also packages for viewgraphs,for simulating the older.UL roffformatters on.UC UNIXand.UC GCOS ,and for other special applications.Typically you will find these packages easier to usethan.UL troffonce you get beyond the most trivial operations;you should always consider them first..PPIn the few cases where existing packages don't do the whole job,the solution is.ulnotto write an entirely new set of.UL troffinstructions from scratch, but to make small changesto adapt packages that already exist..WS.PPIn accordance with this philosophy of letting someone elsedo the work,the part of.UL troffdescribed here is only a small part of the whole,although it tries to concentrate on the more useful parts.In any case, there is no attempt to be complete.Rather, the emphasis is on showing how to do simple things,and how to make incremental changes to what already exists.The contents of the remaining sections are:.sp.nf.in .1i.ta .3i\02.	Point sizes and line spacing\03.	Fonts and special characters\04.	Indents and line length\05.	Tabs\06.	Local motions: Drawing lines and characters\07.	Strings\08.	Introduction to macros\09.	Titles, pages and numbering10.	Number registers and arithmetic11.	Macros with arguments12.	Conditionals13.	Environments14.	Diversions	Appendix: Typesetter character set.sp.in 0.fiThe.UL troffdescribed here is the C-language version running on.UC UNIXatMurray Hill,as documented in [1]..WS.PPTo use.UL troffyou have to prepare not only the actual text you want printed,but some information that tells.ulhowyou want it printed.(Readers who use.UL roffwill find the approach familiar.)For.UL troffthe textandthe formatting information are often intertwined quite intimately.Most commands to.UL troffare placed on a line separate from the text itself,beginning with a period (one command per line).For example,.P1Some text.^ps 14Some more text..P2will change the `point size',that is,the size of the letters being printed,to `14 point' (one point is 1/72 inch) like this:.P1.fiSome text..ps 14Some more text..ps 10.P2.PPOccasionally, though,something special occurs in the middle of a line _to produce.P1Area = \(*p\fIr\fR\|\s8\u2\d\s0.P2you have to type.P1Area = \e(*p\efIr\efR\e\^|\^\es8\eu2\ed\es0.P2(which we will explain shortly).The backslash character.BD  \e is used to introduce.UL troffcommands and special characters within a line of text.