Three husbands (h1, h2, h3) and their wives (w1, w2, w3) want to cross a river.  There is a boat that can hold only two people at a time.  Any husband, any wife, or any couple (husband and wife) can row the boat.  However, there is a catch.  The husbands are jealous; no husband wants a situation where his wife is on a river bank with another husband unless he is present as well.  To win the game, a player must find a schedule of crossings that gets all three couples across the river by step 12.