According to MIT CSAIL
, the XOR wasn't the thing being claimed, rather, it was the frame buffer:The League says this patent can be infringed in "a few lines of a program." It can be, but not on a computer that was commercially available at the time the invention was made. The invention is largely the invention of the frame buffer. As such, it requires hardware which has since become common, making it possible to infringe the XOR claims with a few lines of code. Many, if not most, computer manufacturers including Apple and IBM have taken out licenses which covers programs running on their computers.
If I take this comment at face value, simply making an XOR cursor in your software should not infringe the patent, any more than the invention of a record player makes playing a record an infringement. If hardware already includes a frame buffer, then presumably the hardware has paid for the patent, and you should be free to XOR at will. And if it doesn't, then there's nothing special about using XOR that the patent holder can claim.
glanced at the patent: U.S. Patent 4,197,590. XOR is not mentioned in the claims at all. It is mentioned 31 times in the description, seemingly in the context of how to use the frame buffer (and why the frame buffer is a useful invention).
But, IANAPL. (I am not an apple either) (...though I am an apple eater.)
To the original question, "invention" to me implies a non-obvious effort to connect the dots in a non-trivial manner. "Discovery" implies finding the dots (and their patterns) in the first place.
Figuring out that π is the ratio of circumference to diameter of a circle is a discovery. Using this fact as a tool
to calculate circle parameters is an invention, albeit a trivial (and presumably non-patentable) one.