Um, I forgot to change some of my threes to fours, in my example:
If we imagine a polarised election, where there are four candidates on
one side A B C D and four candidates on the other side W X Y Z, and
four seats, and every ballot is either an ABCD-ballot (ranks every
ABCD above every WXYZ) or an WXYZ-ballot (ranks every WXYZ above every
ABCD) then a bare majority of ABCDs over WXYZs will get all four of
their candidates elected. This would be quite unfair; a better result
would be to elect two of A B C D and two of W X Y Z.
Ian.