X11R4: who has what ???

[root at MCIRPS2.MED.NYU.EDU]

I am confused about distribution/right to use of X11 software.

I understand that sgi offers an x11 developers package, which costs money,
which is partly to pay royalites to the X people(mit ?).

We have a summer student here who is putting up X11R4 from mit which
is available via anonmymous ftp over the net from mit. While we have not
yet gotten the source code to compile, the binaries from the net work fine...
(I don't know if we got the binary object code archives, or if already
compiled and ready to link archives are available).

My question is:

Who owns X for sgi machines ? If it is available over the net, why does
sgi need to sell it ? What are the contractual and legal issues that
a developer such as ourselves should know about the X from sgi or mit ?
Why does sgi sell X for so much(how much ?) when mit has it for free ?

Which package offering is better, or more directly, which should I use
as a sgi software developer ?

dan.
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