Editing Helpmate (section)

=== Duplex ===
{{Chess diagram
|tright
|Milan Vukcevich, June 1961
|  |  |  |  |kl|  |  |nd
|  |  |  |pl|  |pl|  |  
|  |  |  |  |kd|  |  |  
|  |  |  |pd|  |  |  |  
|  |  |  |  |  |  |  |  
|  |  |  |  |  |  |  |  
|  |  |  |  |  |  |  |  
|  |  |  |  |  |  |  |  
|Helpmate in 2: a) Black moves first and White checkmates, b) White moves first and Black checkmates
}}
A further variation is the ''duplex'', another way of getting two problems for the price of one. The first problem is a normal helpmate; the second starts from the same position but has White moving first and helping Black to checkmate him. Again, duplex problems have been composed with other types of problems, but the vast majority are helpmates. To the right is an example by [[Milan Vukcevich]] (from ''CHM avec 6 pieces Bad Pyrmont'', 1996).

The solution with Black moving first is '''1. Ng6 f8=Q 2. Ne5 d8=N#'''. With White moving first, it is '''1. f8=R Nf7 2. d8=B Nd6#'''. These two lines are closely linked, with two white pawn [[promotion (chess)|promotions]] covering the black king's flight squares in the first part and promoted pieces blocking White's flight squares in the second. This problem is an [[Allumwandlung]], a problem in which pawns are promoted to each of knight, bishop, rook and queen.