Unravel this, if you can!

Originally posted by sarathian
But you must tell who moved last? Black or white?

It is part of the problem to work that out. Try both.

Originally posted by BigDoggProblem
T. Volet and P. Wassong
StrateGems 2001
[fen]Nrbb4/qprp3p/PpQK1p1P/RRpp4/Brk2P2/B1P5/1PP5/1N6[/fen]
Release the position
(3 Black Rooks)
(Release the position: Prove that the position is legal, by taking back moves until you reach a position in the past that is obviously legal.)

Solution:

Retract
0...Rb3-b4 -1.Bb4-a3 Ra3-b3 -2.f3-f4 Ra2-a3 -3.Ba3-b4 Ra1-a2 -4.Rb3-b5 Ra2-a1 -5.Bb4-a3 Ra1-a2 -6.Ra3-b3 Ra2-a1 -7.Rb5-a5 Ra1-a2 -8.a5-a6 Qa6-a7 -9.Ra2-a3 Qa7-a6 -10.Ba3-b4 Qa6-a7 -11.Rb3-b5 a7xRb6 -12.Bb4-a3 Qb5-a6 -13.Ba3-b4 Qb4-b5 -14.Ra6-b6 Qb5-b4 -15.Qb6-c6 Qb4-b5 -16.Bc6-a4 Qa4-b4 -17.Rb5-b3 Qb3-a4 -18.Bb4-a3 Qa4-b3 -19.Ra3-a2 Qb3-a4 -20.Ra4-a3 Ra3-a1 -21.f2-f3 Qa2-b3 -22.h5-h6 Rb3-a3 -23.Ra3-a4 Qa1-a2 -24.Ra2-a3 Ra3-b3 -25.h4-h5 Ra4-a3 -26.Ra3-a2 Qa2-a1 -27.h3-h4 Qb3-a2 -28.Ra1-a3 Qa2-b3 -29.Ba3-b4 Rb4-a4 -30.a4-a5 Rb3-b4 -31.Ra5-b5 Rb5-b3 -32.Bb4-a3 Qb3-a2 -33.a2-a4 Qa4-b3 -34.Ba3-b4 Rb4-b5 -35.Rb5-a5 Rb3-b4 -36.Qa5-b6 Rb4-b3 -37.Rb6-b5 Rb3-b4 -38.Bb4-a3 Qb5-a4 -39.Qa3-a5 Qa5-b5 -40.Ba4-c6 Qb5-a5 -41.Rc6-b6 Qb6-b5 -42.Ba5-b4 Rb4-b3 -43.h2-h3 Kb5-c4 -44.Bb3-a4 Rg4-b4 etc.