The puzzle is called MU for a reason. 'Mu' is the valid solution. https://en.wikipedia.org/wiki/Mu_(negative)#The_Mu-koan https://en.wikipedia.org/wiki/Mu_(nega

The puzzle is called MU for a reason. 'Mu' is the valid solution. https://en.wikipedia.org/wiki/Mu_(negative)#The_Mu-koan https://en.wikipedia.org/wiki/Mu_(negative)#The_Mu-koan