Back button on iPhone
There is an opinion that in iPhone apps, there's no point in placing the Back button on screens that are directly accessible via the main navigation menu (at the bottom) - because the button just leads to the main screen, which can be reached with one click on the menu.
On the other hand, the apparent convention is to have the button on these screens, the same as any other screen.
Are there any Apple guidelines concerning this? Or any other authoritative sources?
The iOS HIG doesn't specifically say about the back button on the directly accessible screen, however, just because it happens to be possible to get back to the main screen via the main menu, that doesn't mean that's the best way to do it.
While in the app, returning from deeper screens using the back button should stop at the main screen otherwise you'd go back, back, back - oh! No back button! Context switch - Think - How do I get back to the top - I guess I'll have to use the main menu button.
So I think it should be there.