which vertices of a three-dimensional object would not be visible to a viewer and then not drawing them on the screen, thereby displaying a 3D model that looked solid rather than see-through. Colley created a program that could rotate a solid-seeming cube on the screen, and the trio considered how to make a fun program with it, as students at the lab, including Thompson, had previously created versions of arcade games on the computers. Palmer suggested creating a maze that the user could move through, which he and Colley agreed could work if it was a flat maze composed of cubes where the player's view could only be at 90 degree angles. Colley came back to the other two the next day with the basic Maze program, wherein the player had a goal of traversing the maze to its exit. Palmer and Thompson expanded the game to support two players at once using two PDS-1s linked together with a serial cable, and then added the ability for the two players to shoot one another. Colley added the ability to "peek" around corners without moving because he felt it was too easy to be shot while trying to move and then turn. By the end of 1973, all three developers had left NASA to go to college, and they took the Maze program with them. Thompson went to the Massachusetts Institute of Technology (MIT) beginning in the fall of 1973, while Colley and Palmer went to California Institute of Technology and Stanford University, respectively, at the start of 1974. The game has been inconsistently named both Maze and Maze War: while Thompson and Colley, writing in a 2004 retrospective, refer to it as Maze; Palmer refers to it as Maze War. Later versions of the game also use both names inconsistently, although the PDS-1 source code titles itself "Maze". At MIT, Thompson became involved in computer modeling of dynamic systems at MIT's Project MAC (now the MIT Computer Science and Artificial Intelligence Laboratory), which featured a Digital Equipment Corporation (DEC) PDP-10 minicomputer networked to eight less-powerful PDS-1s for use as graphical terminals. Thompson brought paper tapes of code for several programs from NASA Ames to MIT in February 1974, including Maze. He and co-worker Dave Lebling decided to recreate and expand the game on the Project MAC computer system. Although Lebling does not recall shooting in the version of the game