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"The Staircase Implementation" -- Leonard (Johnny Galecki, right) tells Penny about how he and the guys (Kunal Nayyar, left; Simon Helberg, center) met Sheldon for the first time...and what happened to the elevator, on THE BIG BANG THEORY, Monday, May 17 (9:31-10:01 PM, ET/PT) on the CBS Television Network. Photo: Robert Voets/CBS ©2010 CBS Broadcasting Inc. All Rights Reserved.