This is not a good situation. The FSF took Berkeley's YACC and GPL'ed
it[*].
I think you are mistaken. We have never done anything with BYACC as
far as I know.
[*] to the displeasure of Robert Corbett, the Byacc author.
I don't believe this either. We used some of his code once,
and he gave us his explicit cooperation with that.