In June 1977, Marc Blank, Bruce K. Daniels, Tim Anderson, and Dave Lebling began writing the mainframe version of "Zork" (also known as "Dungeon"), at the MIT Laboratory for Computer Science, directly inspired by "Colossal Cave Adventure". The game was programmed in a computer language called MDL, a variant of LISP. The term Implementer was the self-given name of the creators of the text adventure series Zork. It is for this reason that game designers and programmers can be referred to as an implementer, often shortened to Imp, rather than a writer. In early 1979, the game was completed. Ten members of the "MIT Dynamics Modelling Group" went on to join Infocom when it was incorporated later that year. In order to make its games as portable as possible, Infocom developed the Z-machine, a custom virtual machine that could be implemented on a large number of platforms, and took standardized "story files" as input. In a non-technical sense, Infocom was responsible for developing the interactive style that would be emulated by many later interpreters. The Infocom parser was widely regarded as the best of its era. It accepted complex, complete sentence commands like "put the blue book on the writing desk" at a time when most of its competitors parsers were restricted to simple two-word verb-noun combinations such as "put book". The parser was actively upgraded with new features like undo and error correction, and later games would 'understand' multiple sentence input: 'pick up the gem and put it in my bag. take the newspaper clipping out of my bag then burn it with the book of matches'.