>By my understanding of the question the 4th line will result in the missionary being eaten

>>(c=cannibal, m=missionary)
>>left - on boat - right
>>cccmmm -
>>ccmm - cm
>>ccmm - m - c
>>cmm - cm - c
>----------^^^^^^

>2 Canibals and 1 missionary - Stew!

The cm is a cannibal and a missionary on the boat, and one cannibal on each back of the river.

My girlfriend had a better solution where a cannibal drives the boat back and forth - it naturally seperates the cannibals into singles.