The U.S. Patent and Trademark Office has granted numerous software patents on software techniques. Patents are an absolute monopoly--independent reinvention is precluded. This monopoly lasts for seventeen years, i.e., forever (with respect to computer science).
One patent relevant to TeX is patent 4,956,809, issued to the Mark Williams company on September 11, 1990, applied for in 1982, which covers (among other things)
representing in a standardized order consisting of a standard binary structure file stored on auxiliary memory or transported on a communications means, said standardized order being different from a different order used on at least one of the different computers;
Converting in each of the different computers binary data read from an auxiliary data storage or communications means from the standardized order to the natural order of the respective host computer after said binary data are read from said auxiliary data storage or communications means and before said binary data are used by the respective host computer; and
Converting in each of the different computers binary data written into auxiliary data storage or communications means from the natural order of the respective host computer to the standardized order prior to said writing.
... in other words, storing data on disk in a machine-independent order, as the DVI, TFM, GF, and PK file formats specify. Even though TeX is "prior art" in this respect, the patent was granted (the patent examiners not being computer scientists, even less computer typographers). Since there is a strong presumption in the courts of a patent's validity once it has been granted, there is a good chance that users or implementors of TeX could be successfully sued on the issue.
As another example, the X window system, which was intended to be able to be used freely by everyone, is now being threatened by two patents: 4,197,590 on the use of exclusive-or to redraw cursors, held by Cadtrak, a litigation company (this has been upheld twice in court); and 4,555,775, held by AT&T, on the use of backing store to redraw windows quickly.
Here is one excerpt from a recent mailing by the League for Programming Freedom (see section What to do?) which I feel sums up the situation rather well. It comes from an article in Think magazine, issue #5, 1990. The comments after the quote were written by Richard Stallman.
"You get value from patents in two ways," says Roger Smith, IBM Assistant General Counsel, intellectual property law. "Through fees, and through licensing negotiations that give IBM access to other patents.
"The IBM patent portfolio gains us the freedom to do what we need to do through cross-licensing--it gives us access to the inventions of others that are the key to rapid innovation. Access is far more valuable to IBM than the fees it receives from its 9,000 active patents. There's no direct calculation of this value, but it's many times larger than the fee income, perhaps an order of magnitude larger."
This information should dispel the belief that the patent system will "protect" a small software developer from competition from IBM. IBM can always find patents in its collection which the small developer is infringing, and thus obtain a cross-license.
However, the patent system does cause trouble for the smaller companies which, like IBM, need access to patented techniques in order to do useful work in software. Unlike IBM, the smaller companies do not have 9,000 patents and cannot usually get a cross-license. No matter how hard they try, they cannot have enough patents to do this.
Only the elimination of patents from the software field can enable most software developers to continue with their work.
The value IBM gets from cross-licensing is a measure of the amount of harm that the patent system would do to IBM if IBM could not avoid it. IBM's estimate is that the trouble could easily be ten times the good one can expect from one's own patents--even for a company with 9,000 of them.