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From: rick@uunet.UU.NET (Rick Adams)
Subject: [gnu.misc.discuss...] Re: Imagine if you couldn't use compress any more
Message-ID: <1990Aug6.034503.24333@math.lsa.umich.edu>
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Sender: emv@math.lsa.umich.edu (Edward Vielmetti)
Reply-To: rick@uunet.UU.NET (Rick Adams)
Organization: University of Michigan, Department of Mathematics
Date: Mon, 6 Aug 90 03:45:03 GMT
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Archive-name: lzw-patent/05-Aug-90
Original-posting-by: rick@uunet.UU.NET (Rick Adams)
Original-subject: Re: Imagine if you couldn't use compress any more
Archive-site: uunet.uu.net [192.48.96.2]
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Reposted-by: emv@math.lsa.umich.edu (Edward Vielmetti)

The text for patent "4,558,302 Dec. 10, 1985 Welch" can be ftped from
uunet.uu.net as pub/lzw-patent.Z

It's fun (and virtually indecipherable) reading. For example, they claim

	   10. The compression apparatus of claim 5 further including
	initializing means for storing in the locations of said memory
	means an empty indicia signal representing that the location
	storing said empty indicia signal is empty, said empty
	indicia signal having a value not equal to any compressed code
	signal.

or, as best as I can figure out

	int table[N]

	for(i=0;i<n;i++)
		table[i] = NIL;

is one of their intellectual property claims. (So be careful about
initializing your tables!)

There are 181 claims, many as specious as this (and many probably legitimate
"invention").

--rick