[Retros] Add units: 15th update

[Alain BROBECKER]

Dear retro friends,

A new update of the "Add units" booklet can be found here:
http://abrobecker.free.fr/chess/addunits.pdf
 
Modified N2Ai (previous version cooked by Mu-Tsun Tsai)
and 2A which was improved.

Regarding N2Ai, here's another version:
Alain Brobecker & Computer, Original 2011/04/04
4Q3/2Q5/7Q/Q3Q3/4Q3/1Q6/6Q1/5Q2
http://www.janko.at/Retros/d.php?ff=4Q3/2Q5/7Q/Q3Q3/4Q3/1Q6/6Q1/5Q2
It has 11 squares that are controlled twice, but i prefer
the one in the booklet since it has BK not on the edge and
7 squares controlled twice (no position with >7 has
solution with BK inside).

Best regards, Alain