[r-t] Extents with two fixed hunt bells

[Nicholas Small]

Some time ago, in response to a query from me, Richard Smith produced some doubles principles with three lead extents. After 40 
changes, two bells are home, having occupied each possible pair of positions once.

For a major method that could produce an extent without affecting the two hunts, the number of changes in a division/lead would 
have to be a multiple of 56.

Nicholas Small

(Apologies if this has been mentioned already - I'm a couple of weeks behind with
the digests.)