Answer: The first three volumes were stunning. It wasn’t until a new edition of Volume 2 was to be reset with primitive digital type instead of the traditional metal type of the earlier editions that there was a problem. Horrified by the inferior results, Knuth took it upon himself to improve things. After all, digital type was software, right? Determined to develop a solution, Knuth stopped work on his books and devoted himself to typography for the next 10 years. The result: The TeX typesetting system and the Metafont font description language. The combination of the two offered powerful typographic control that hasn’t been matched (even today), especially for complex typesetting like mathematical formulas.