yacc: public domain?

[Ron Natalie]

If yaccpar was merely copyrighted, you could use the algorithms gleaned
from it to your hearts content.  The copyright doesn't apply to the idea
only the words.  The point is that the UNIX source code, as has been
beaten to death here, is a trade secret.  Your installation was given
the code with the restriction that you do not divulge how it works.
Following this strictly means that just rewriting AT&T's algorithm is
in violation of your agreement.

-Ron