[1]: 77–78 It makes only two cuts, so each partner receives a single connected piece.
Initially, each partner makes a vertical cut such that the cake to its left is worth for him exactly 1/3.
The remainder has to be divided between the remaining partners (Bob and Carl).
The challenge is to make sure Alice won't envy any of them.
Hence, by the intermediate value theorem, there must be an angle in which Bob thinks the pieces from both sides of the knife are equal.
The rotating-knife procedure can be adapted for chore division - dividing a cake with a negative value:[1]: exercise 5.10 in the initial step, The rightmost cut should be selected, instead of the leftmost cut.