Load ipynb contained from a different directory

Let us suppose my main notebook (main.ipynb) is next to a folder otherpath containing another notebook to be imported (to_be_imported.ipynb).

If I do
`import ipynb.fs.defs.otherpath.to_be_imported`

I get
`ModuleNotFoundError: No module named 'ipynb.fs.defs.otherpath'`

If I move to_be_imported.ipynb in the same folder of the main file, everything works.

Start with the import entry point `ipynb.fs.defs.otherpath.to_be_imported` and compare it with importing `to_be_imported.ipynb` from the same directory. Reproduce the `ModuleNotFoundError` using `main.ipynb` and the `otherpath` folder; done means the nested notebook imports successfully.

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