+=3: A Controversial but Nevertheless Logical Adventure

+=3: A Controversial but Nevertheless Logical Adventure is an interactive fiction game, written as a counter-example to a claim made on the rec.arts.int-fiction newsgroup that "there could be no puzzles which are logical yet unsolvable". The game essentially has one puzzle, but one that - as the authors believe - is practically impossible to solve despite making perfect logical sense.

The player takes control of an adventurer who has already solved all the puzzles in the game, and now faces one last challenge, a "Three Troll" guarding a bridge. In the player's inventory is a "qualitative calculator", and the player also knows that "something is ticking" in the vicinity. The goal is to get past the troll.