directory structure

when i install ci4 using composer, it creates the struture shown below. I presume my app goes in the top level app so whats the reason for vendor/codeigniter/framework/app and the other duplicates? can i delete the duplicates (keeping the system of course)?
thanks, Bill
app
........config
........controllers
public
tests
vendor
........bin
........codeigniter4
................framework
........................app
................................config
................................controllers
........................public
........................system
........................tests
........................writable
........composer
........fakerphp
........ad nauseum
writable

There's a definite destinction using Composer or a stand-alone installation as described here:
https://codeigniter4.github.io/userguide...anual.html
If you don't need the additional 'luggage' I suggest you install it the manual way.
Note that it may make future upgrades more difficult..

"the manual way. .....may make future upgrades more difficult." which is why i want to do it the right way starting off ie use composer. My query was what is the reason for the duplicate directories, can i safely delete them or does the world go into melt down
Bill

Everything under /vendor is the code installed by composer.  You can usually just ignore that. You normally do not need to change anything down there unless doing Codeigniter development.

thanks, I still don't understand the need for the duplicate folders to exist so i'll just ignore them.
Bill

Yes, "vendor/codeigniter/framework/app" or others are not needed for running your app.

But you can get the latest files from them.
Without those files, the status of the latest files is not known, so project files cannot be automatically updated
by https://github.com/tattersoftware/codeigniter4-patches

ci-phpunit-test | CodeIgniter Testing Guide | CodeIgniter 3 to 4 Upgrade Helper

Many thanks, that was the sort of explanatory answer I was hoping for.
Bill