How do you detach the 2nd screen from within another screen?

ctrl-a a d

ctrl+a a will pass the escape sequence (ctrl+a) to the sub-screen.. So, ctrl+a a d will do ctrl+a d in the sub-screen (detaching it)

It works with any screen command, for example ctrl+a, a, c will create a window in the sub-screen

In general, if you have a screen s3 within another screen s2 within another screen s1, you can execute a command ctrl-a d in the screen:

• s1 by doing: ctrl-a d

• s2 by doing: ctrl-a a d

• s3 by doing: ctrl-a a a d

• ...