September 1999

Rewriting the Bible in 0's and 1's

Continued from page 1

By Steve Ditlea

Knuth took it upon himself to write every line of code for software that yielded beautiful typography. He drew the name of his typesetting program from the Greek word for art-the letters are tau epsilon chi (it rhymes with "blecch"). Says Knuth: "Well over 90 percent of all books on mathematics and physics" are typeset with TeX and with its companion software, Metafont, a tool Knuth developed to design pleasing type fonts.

He is quick to acknowledge the contribution of the type designers, punch cutters, typographers, book historians and scholars he gathered at Stanford while developing TeX. Some are in the audience. He tells them: "TeX is what we now call open-system software-anybody around the world can use it free of charge. Because of this, we had thousands of people around the world to help us find all the mistakes. I think it's probably the most reliable computer program of its size ever."

Anyone who doubts this claim by the decidedly unboastful Knuth can find confirmation from Guy Steele, one of TeX's first users and now a distinguished engineer at Sun Microsystems. TeX, says Steele, was one of the first large programs whose source code was published openly. Steele says Knuth's publication of the TeX code in a book, along with full comments, made it so that "anyone could understand how it works and offer bug fixes." With academe's top scientists and mathematicians as beta-testers, an extraordinary quality control team helped perfect TeX. (The TeX development effort was a model for today's open-source software movement, which has given the world Linux-an operating system that is beginning to compete with Microsoft Windows.)

Perfectability is a major preoccupation of Knuth's. The only e-mail address Knuth maintains gathers reports of errata from readers of his books, offering $2.56 for each previously unreported error. (The amount is an inside joke: 256 equals 2 to the 8th power-the number of values a byte can represent.) Knuth's reward checks are among computerdom's most prized trophies; few are actually cashed.

He takes this error business very seriously. Engraved in the entryway to his home are the words of Danish poet Piet Hein:

The road to wisdom?
Well it's plain
and simple to express:

Err
and err
and err again
but less
and less
and less.

In a variation on this theme of perfectability, Knuth's contribution to computer science theory in the pages of The Art of Computer Programming has been his rigorous analysis of algorithms. Using methods in his book, the operations used to translate machine instructions into equations can be tested to determine whether they are optimal. Improving a program then becomes a question of finding algorithms with the most desirable attributes. Not that theoretical proofs can replace actually running software on a computer. In an often-cited remark he mentions on his Web page, he once warned a colleague: "Beware of the above code; I have only proved it correct, not tried it."