what songs did lady gaga write for Britney Spears?

i know that she worked with Britney on circus but which individual songs did she help write?

It was only “Quicksand.”

http://en.wikipedia.org/wiki/Circus_(Britney_Spears_album)

Search for Stefani Germanotta ^

Lady Gaga & Darkchild – In the Studio w/ TELEPHONE.