>I don't think I thought it out as thoroughly as you did. You have to consider, amongst others, the possibility of his sister being, say, also his aunt - or even his grandma! :-)
That reminds me of the story of a witness who was asked at court whether he had any relatives, to which he replied: "No, my only sister died 150 years ago."
It turned out his father had married young, and had a daughter who died soon. Then, his father had married again at an old age - something like 80 or 90 years - and the witness in question (his fathers son from this second marriage) was also quite old when he was questioned.
Difference in opinions hath cost many millions of lives: for instance, whether flesh be bread, or bread be flesh; whether whistling be a vice or a virtue; whether it be better to kiss a post, or throw it into the fire... (from Gulliver's Travels)
