That is a common statement to not have each use the other... but there is nothing wrong with doing so... and in this case it makes good sense...
In the real case, libs and dbg... I would have to copy various libs subs into the dbg module to avoid the loop. which would cause duplication of code, which is also a never do...
And since the two modules come together it is okay for them to rely on each other.
in a certain sense, dbg is like a class that is being inherited, and libs is just a general module of subs to be used by anyone. So for them to be interdependent isn't really a problem for the design...