A long time ago (1991) Wolfram got upset when someone tried to implement Mathematica. Now there is the Wolfram Language. Are there any constraints (for example, legal constraints) on implementing the Wolfram Language? Of course I am not talking about the obvious constraints of intelligence, time and effort. Are there things that can't be done when trying to implement the Wolfram Language? Does anyone have experience with this?
I know that Mathics is implemented under GPL3 and they hired the guy who did it. This would seem to indicate to me that wolfram won't send threatening letters to someone who implements part of the Wolfram Language under the GPL.
If any of you know of any documents from Wolfram setting a precedent related to this, I would like to know it. If you work at Wolfram and are reading this post, I would like some clear guidance on this issue.