three bodies of work that he considered to be standards of excellence for mathematical typography: the books typeset by the Addison-Wesley Publishing house (the publisher of The Art of Computer Programming) under the supervision of Hans Wolf; editions of the mathematical journal Acta Mathematica dating from around 1910; and a copy of Indagationes Mathematicae, a Dutch mathematics journal. Knuth looked closely at these printed papers to sort out and look for a set of rules for spacing. While TeX provides some basic rules and the tools needed to specify proper spacing, the exact parameters depend on the font used to typeset the formula. For example, the spacing for Knuth's Computer Modern fonts has been precisely fine-tuned over the years and is now set; but when other fonts, such as AMS Euler, were used by Knuth for the first time, new spacing parameters had to be defined. The typesetting of math in TeX is not without criticism, particularly with respect to technical details of the font metrics, which were designed in an era when significant attention was paid to storage requirements. This resulted in some "hacks" overloading some fields, which in turn required other "hacks". On an aesthetics level, the rendering of radicals has also been criticized. The OpenType math font specification largely borrows from TeX, but has some new features/enhancements. Hyphenation and justification In comparison with manual typesetting, the problem of justification is easy to solve with a digital system such as TeX, which, provided that good points for line breaking have been defined, can automatically spread the spaces between words to fill in the line. The problem is thus to find the set of breakpoints that will give the most visually pleasing result. Many line-breaking algorithms use a first-fit approach, where the breakpoints for each line are determined one after the other, and no breakpoint is changed after it has been chosen. Such a system is not able to define a breakpoint depending on the effect that it will have on the following lines. In comparison, the total-fit line-breaking algorithm used by TeX and developed by Donald Knuth and Michael Plass considers all the possible breakpoints in a paragraph, and finds the combination of line breaks that will produce the most globally pleasing arrangement. Formally, the algorithm defines a value called badness associated with each possible line break; the badness is increased if the spaces on the line must