Historically, the first protocol allowing to accomplish such a task was devised independently by John Selfridge and John Conway.

1. Thierry cuts the cake into three pieces he thinks equally large.
2. Hugo considers the two biggest pieces ; if one seems bigger than the other one, he equalizes it and sets the leftover aside.
3. Carolines takes a piece, then Hugo (if he equalized a piece during the previous step he has to pick it if Caroline didn't), then Thierry.
4. If there was no equalization, game over. Else the one from Hugo and Caroline who tooked the untrimmed piece cuts the leftover into thirds.
5. Pick one piece from the leftover, in that order : the one who took the trimmed piece, Thierry, the one who cut the leftover.

This problem, presented by Hugo Steinhaus, has been solved for n people but protocols devised for n>3 are not obvious to put in practice (eg with 22 people the first step is to cut the cake into more than one million pieces).