How to close split window / adjacent editor - Xcode 4

Question

I've managed, by playing around with the menus in Xcode 4, to open a window in an adjacent editor (Navigate, open in adjacent editor). Unfortunately, I'm having trouble figuring out how to close that window. How do you do that?

Answer 1

Cmd+Enter

or View -> Standard Editor -> Show Standard Editor

Answer 2

I fixed this by going to 'view > editor > standard' and this reset the view to the standard one window view. I have yet to figure out why the x in the upper right corner of the new window is grayed out. Not a perfect solution, but a solution.