Z:gnu-www-ja-stallman-mec-india--de64bc-In fact you can't tell what a/en

In fact you can't tell what a software patent covers even roughly, except by studying it carefully. This is different from patents in other areas, because in other areas there is some physical thing happening, and the details of that physical thing usually give you a sort of anchor so that you can tell whether it relates or not. But in software there is no such thing, and so it's easy for two totally different ways of saying something to cover, in fact, the same computation, and it takes careful study to see that they cover the same one. Because of this, even the patent office can't keep track. So, there is not one, but two patents covering LZW data compression. The first one was issued in 1985 and I think the second one in 1989. But that one I think had been applied for even earlier. One of these patents belongs to Unisys and the other belongs to IBM.