[Retros] new Type DD problem + 3 improved problems

[Andrew Buchanan]

Dear retro friends,

Here are four easy "Type DD" problems. I.e. they all have the stipulation
"Last move? Duplex" and the last move turns out to be the same kind for
White as for Black.

First the improvements:

(1) Quick fix to remove 3 units:
www.janko.at/Retros/d.php?ff=3brn1N/2ppRKPk/4pp1p/8/8/8/8/8
(4+9) Last move? Duplex
version of Mario Richter

(2) Quick fix to remove 1 unit:
www.janko.at/Retros/d.php?ff=8/Pp2p3/kpp5/1p6/1P6/KPP3P1/pP2P3/8
(8+7) Last move? Duplex

(3) New approach:
www.janko.at/Retros/d.php?ff=NK6/P1pp4/qp6/Bp6/BP6/QP6/b1PPP1P1/nk6
(12+8) Last move? Duplex

And a new one:

(4) One of the two outstanding tasks:
www.janko.at/Retros/d.php?ff=bR1QB3/bn1qpp2/Bpkp4/n1p5/N1P5/1PKP4/bN1QPP2/Br
1qb3
(14+15) Last move? Duplex

This is the 56th DD record, leaving us just one outstanding DD task (apart
from castlings & en passant, which seem impossible), namely: QxQ.

All the best,
Andrew