[Retros] Add pieces

Noam Elkies elkies at math.harvard.edu
Sat Mar 12 01:18:41 EST 2011

Theodore Hwa <hwatheod at cs.stanford.edu> writes:

>> it would be difficult to compose a problem in which it is not

>> possible to add an additional piece (although not impossible).

> Here's one possibility with 30 units, nobody in check:

> Starting from the initial position, remove the queens,

> and move the kings over to the queens' original squares.

> It is not possible to add any pieces.

Neat. Possibly reducible to 28: move each King one square further,
removing the Bc1 and Bc8. Or even 26, going back to T.Hwa's position
but putting a2,h2,a7,h7 on b3,g3,b6,g6 and removing all four Knights
(or some suitable combination of Knights and Rooks). 26 could then
also be attained by a mixture of the two techniques: put the Kings
back on c1 and c8, and play only h2xg3 and h7xg6; or put just wK on c1
and add a7xb6.


P.S. Take the above with a grain of salt since it's well past my normal
bedtime here...

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