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It would look like a coincidental case of parallel evolution when Larry Shanker of Salem, OH began selling his map pack, "Duke's Next Adventure", the following year for the same price.
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One Tony Kamin of Green Bay, WI seems to have reverse-engineered the DN map format and gotten a level editor together as early as 1992, shopping around two alternate level sets under the name "Duke Nukem Extension Set" for only five dollars' registration a piece. While it would later become a standard matter of course that companies would form solely to sell new level packs to iD Software's first-person shooters, a couple of enterprising individuals led the vanguard as early as Duke Nukem 1, before there was the same calibre of groundbreaking excellence to co-opt. Duke Nukem for DOS (full version, all three episodes) was included on the Duke Nukem 3D for DOS CD.
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