Apple MacBook Pro (17-inch, Early 2009) - Manual (Page 29)

Chapter 2 Life with Your MacBook Pro 29
 Three-finger swipe lets you rapidly page through documents, move to the previous or
next photo, and more.
 Four-finger swipe works in the Finder and all applications. Swiping four fingers to the
left or right activates Application Switcher so you can cycle through open
applications. Swiping four fingers up or down causes Exposé to show the desktop or
display all open windows.