  Yasutaka Nakanishi asked in 1981 whether a 3-move is an unknotting operation.
In Kirby's problem list, this question is called `The Montesinos-Nakanishi
3-move conjecture'. We define the n-th Burnside group of a link and use the 3rd
Burnside group to answer Nakanishi's question; ie, we show that some links
cannot be reduced to trivial links by 3-moves.
