There are many unsolved questions in the world: Are colours all in our mind? What's the probability the sun will rise tomorrow? How has James Corden forged a successful career as a comic? These posers have stumped even the brainiest of the world's boffins for years.
At the turn of the century, the Clay Mathematics Institute launched the Millennium Prize, a million dollar incentive with the aim of answering seven of the subject's trickiest conundrums. Only one has been unraveled, but the assumption is that all are solvable.
The reward may focus strictly on maths problems, but it should extend its remit to include arguably society's greatest riddle: which is the best Super Mario game? Even the eggheads at the institute know it's an impossible question.
You might as well ask a parent which is their favourite child, but even they know that answer, deep down. Trying to pick out the finest of the portly plumber's outstanding oeuvre? It's a real mustache-twirler.
It might not make me a millionaire, but seeing as it's Mario Day (no, really), now is the time to ask (and indirectly justify Nintendo's forced celebration): Which are Mario's Koopa bloopers, and which are the shining power stars?