To avoid any hint of copyright infringement, a team reimplementing an API (or similar) must never have looked at the original code.

https://en.wikipedia.org/wiki/Clean_room_design

The usual term is "Chinese Wall" [1].

[1] https://en.wikipedia.org/wiki/Chinese_wall

means a group check the source and documents. Another group never sees the code, only the documentation, and proceed to implement whatever they need being able to say that they have not used the original code.

This is common in reverse engineering stuff.