.NHExperience.PPThere are really three aspects of interest_howwell.UC EQNsets mathematics,how well it satisfies its goalof being ``easy to use,''and how easy it was to build..PPThe first question is easily addressed.This entire paperhas been set by the program.Readers can judge for themselveswhether it is good enough for their purposes.One of our users commented that although the outputis not as good as the best hand-set material,it is stillbetter than average,and much better thanthe worst.In any case, who cares?Printed books cannot compete with the birds and flowersof illuminated manuscripts on esthetic grounds,either,but they have some clear economic advantages..PPSome of the deficiencies in the output couldbe cleaned up with more work on our part.For example, we sometimes leave too much space betweena roman letter and an italic one.If we were willing to keep track of the fontsinvolved,we could do this better more of the time..PPSome other weaknesses are inherent in our output device.It is hard, for instance, to draw a lineof an arbitrary length without gettinga perceptible overstrike at one end..PPAs to ease of use,at the time of writing,the system has been used by two distinct groups.One user population consists of mathematicians,chemists, physicists, and computer scientists.Their typical reaction has been something like:.IP " (1)"It's easy to write, although I make the following mistakes....IP " (2)"How do I do...?.IP " (3)"It botches the following things.... Why don't you fix them?.IP " (4)"You really need the following features....sp 5p.PPThe learning time is short.A few minutes gives the general flavor,and typing a page or two of a paper generallyuncovers most of the misconceptions about how it works..PPThe second user group is much larger,the secretaries and mathematical typistswho were the original target of the system.They tend to be enthusiastic converts.They find the language easy to learn(most are largely self-taught),and have little trouble producing the output they want.They are of course less critical of the esthetics of their outputthan users trained in mathematics.After a transition period, most findusing a computer more interesting thana regular typewriter..PPThe main difficulty that users have seems to be rememberingthat a blank is a delimiter;even experienced users use blanks where they shouldn't and omit themwhen they are needed.A common instance is typing.P1f(x sub i).P2which produces.EQf(x sub i).ENinstead of.EQf(x sub i ).ENSince the .UC EQNlanguage knows no mathematics, it cannot deduce that theright parenthesis is not part of the subscript..PPThe language is somewhat prolix, but this doesn't seemexcessive considering how much is being done,and it is certainly more compact than the corresponding.UC TROFFcommands.For example, here is the source for the continued fractionexpression in Section 1 of this paper:.P1.ne 4.ce 0     a sub 0 + b sub 1 over       {a sub 1 + b sub 2 over         {a sub 2 + b sub 3 over           {a sub 3 + ... }}}.P2This is the input for the large integral of Section 1;notice the use of definitions:.P1.ce 0.ne 15.in 1define emx "{e sup mx}"define mab "{m sqrt ab}"define sa "{sqrt a}"define sb "{sqrt b}"int dx over {a emx - be sup -mx} ~=~left { lpile {     1 over {2 mab} ~log~            {sa emx - sb} over {sa emx + sb}   above     1 over mab ~ tanh sup -1 ( sa over sb emx )    above     -1 over mab ~ coth sup -1 ( sa over sb emx )}.in 0.P2.PPAs to ease of construction,we have alreadymentioned that there are really only a few person-monthsinvested.Much of this time has gone into two things_fine-tuning(what is the most esthetically pleasing space to usebetween the numerator and denominator of a fraction?),and changing things found deficient by our users(shouldn't a tilde be a delimiter?)..PPThe program consists of a number of small,essentially unconnected modules for code generation,a simple lexical analyzer,a canned parser which we did not have to write,and some miscellany associated with input filesand the macro facility.The program is now about 1600 lines of .UC C[6], a high-level language reminiscent of.UC BCPL .About 20 percent of these lines are ``print'' statements,generating the output code..PPThe semantic routines that generate the actual .UC TROFFcommands can be changed to accommodate other formatting languagesand devices.For example, in less than 24 hours,one of us changed the entire semantic packageto drive .UC NROFF,a variant of.UC TROFF,for typesetting mathematics on teletypewriter devicescapable of reverse line motions.Since many potential users do not have accessto a typesetter, but still have to type mathematics,this provides a way to get a typed version of the final outputwhich is close enough for debugging purposes,and sometimes even for ultimate use.