> If there's a single IB file that has not been deleted and written in
> another way that doesn't constitute derivative work, the IPL will
> remain in that file.

Allow me to add to this:

My understanding of US law is that it is not necessary for the file to
be deleted and recreated. It is enough for all of the source code to
change over time, so that no original copyright remains.

This does not mean that every line needs to change. There is "fair use"
quotations and the right to reverse engineer API's. Also, there is a
specific methodology to be used for comparing source code in US courts.
Trivial formating changes or variable renaming must be ignored but also
the comparison must ignore similarities dictated by function (two
bubble sort routines are going to look pretty similar, even if
developed independently).

> The two licenses will coexist for a lot of time.

Yes, years for sure, but it may be shorter than we think.

Paul


Paul