[Retros] Task - double check mate - NECESARY

[raosorio at fibertel.com.ar]

Gianni Donatti proposed the following version of the double-check mate PG.
It's a fact that in the previous one the knight check is not necesary to checkmate
but it's the way to get the task in 6 moves. I think Gianni's is the shortest extending
the meaning of the task to 'necesary double-check'.

Hi Roberto -

Here's a version of your double-check pg in which both checks are required.  In a way...

1. Cg1-f3   Pa7-a5     2. Cf3-e5   Ta8-a6     3. Pf2-f3   Ta6-d6    
4. Re1-f2   Td6-d3     5. Rf2-g3   Pd7-d6     6. Ce5-d7   Pe7-e5    
7. Rg3-g4   Cg8-e7     8. Rg4-g5   Pg7-g6     9. Rg5-f6   Ce7-g8