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The conduct of a new sedoretu is to some extent, and wisely, prescribed by custom and sanctioned by religion. The first night after the ceremony of marriage belongs to the Morning and Evening couples; the second night to the Day and Night couples. Thereafter the four spouses may join as and when they please, but always and only by invitation given and accepted, and the arrangements are to be known to all four. Four souls and bodies and all the years of their four lives to come are in the balance in each of those decisions and invitations; passion, negative and positive, must find its channels, and trust must be established, lest the whole structure fail to found itself solidly, or destroy itself in selfishness and jealousy and grief.
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Ursula K. Le Guin (The Birthday of the World and Other Stories)