While we've been telling jaded partners and family members for ages, it looks like there's some -- slightly obscure -- proof. The researchers reconstructed their own levels, forcing gamers to choose between one of two paths, with a mix of power-ups, health items and enemies that created a "logical statement". If you can complete the level with that particular combination, then it would resolve the Boolean satisfiability problem -- a logic puzzle that squares variables against whether a statement is true, and whether the same can be said of all similarly composed statements. While the theory sounds trickier than the first stage of Mario, Nintendo's flagship title -- as well as Donkey Kong, Legend of Zelda, Metroid and the Pokémon series -- were categorized as NP-hard. This means deciding if a player can solve a certain part of the game is at least as hard as the most difficult problems in NP; a classification that involves easy-to-check, difficult-to-solve propositions. While you figure out what that means, we're hitting up Nintendogs 3D. Because we like a challenge.