Propositiones ad Acuendos Juvenes/Problems/17 - De Tribus Fratribus Singulas Habentibus Sorores

by : Problem $17$

 * De Tribus Fratribus Singulas Habentibus Sorores: Three Friends and their Sisters
 * Three friends, each with a sister, needed to cross a river.
 * Each one of them coveted the sister of another.
 * At the river, they found only a small boat, in which only two of them could cross at a time.


 * How did they cross the river, without any of the women being defiled by the men?

Solution
The constraint here is that at no time may a man be on the same bank as (or in the boat with) the sister of another, without the brother of that sister being present as well.

Let $M_1$, $M_2$ and $M_3$ denote the men, and $S_1$, $S_2$ and $S_3$ denote their respective sisters.

Let them be crossing from $A$ to $B$.

As follows:

Also presented as
This can also be presented as men with their wives, rather than sisters.