Enforcing the GPL with Judo moves

“The intent of free software is to render the code that runs the
machines that run our lives transparent. In the words of Lawrence
Lessig, free software is “free in the sense that the control coders
build be transparent to all, and that anyone have the right to take
that control, and modify it as he or she sees fit.”

The mechanism by which free software achieves this is copyleft.
Copyleft is a hack on copyright law that takes away the exclusive
rights of the copyright holder and shares them with the user, who
is given the right to modify, copy, share and redistribute the
software, but must pass on the same rights to any subsequent
users.

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