Challenge No. 5 Is there any position which is A1.3 illegal by virtue of having only A1.3 illegal prior positions, but has no dead prior position? A regular DR illegal position, with all prior positions dead, is termed a Gen 0 position. However, it is also possible that all prior positions are DR illegal. We use the term Gen x, for x >= 1, to refer to a position where the last x generations of prior position are DR illegal themselves. BRRBQK1k/1PPPPPp1/5pPb/5Pp1/6P1/8/8/8 w - - id #047 (14+5) Noam Elkies. Whose move?; This position has two A1.3 Generation 1 illegal prior positions. The following simpler position has only one: NRRQBK1k/BPPPPPp1/1P3pPb/6pP/8/8/8/8 w - - id #047a (15+5) Noam Elkies Whose move?; Another, very different position has been found: KBb1kb1r/PpPppppp/1p6/p7/8/8/8/8 w - - id #063 (4+10) Richard Stanley. White to move. Last move? Castling rights?; An extension by Noam Elkies takes this to Gen 3! rrbK4/kp3q2/pb2p3/2Pp2p1/Pn1Pp1P1/4p1P1/4P1PB/5BRR w - - id #069 (12+14) Richard Stanley version by Noam Elkies. Legal?; What about later generations? There is still much exploration to do... I randomly conjecture that there are no Gen 4+ positions. Prove me wrong!