Challenges Some people like to solve chess problems, others like to create them. This page is to support the latter class of individual, by stating the state of the art. Here is a list of challenges which are currently open, or have only recently been solved. For some of them, you can drill down to find information about the current status. Older  challenges can be found here. (1) Is there an existing problem which A1.3 impacts in an interesting way? [i.e. not a problem where A1.3 merely truncates a line of play.] (2) What forward moves can be proved legal or illegal by use of A1.3? [Under a wide range of circumstances, castling and e.p. can be proved either legal or illegal, in DR restricted positions.] (3) What is the maximum number of pieces which can be found in an A1.3 illegal/restricted position? (4) What is the maximum number of shots in an A1.3 illegal/restricted position? [Current record 30, but only 8 are essential. Surely we can do better than this.] (5) Is there a position which illegal by virtue of having an A1.3 illegal prior position, i.e. has no merely dead prior position? Follow-up is: how far deep can one go: how many shots may you have to go back from an A1.3 illegal position in order to reach a legal dead position? (6) Are there any really weird paradoxes lurking in here? There are known paradoxes in traditional retro, involving castling and e.p. conventions. Now assume that we put aside or modify those conventions. What kind of weird dependencies are nevertheless possible? [Castling is definitely an issue. e.p. isn't.] (7) Can we get an exhaustive list of all A1.3 illegal/restricted positions with 2, 3, 4... pieces? (8) What is the shortest proof game leading to an A1.3 illegal position? (9) Is it meaningful to ask how many different types of blocked position are there? How many of these can be translated into problems? (10) Is there a pure Class 1 problem which starts with enough material for checkmate? [Yes #083 has way more than enough material, with 24 units on the board.] (11) Is there a problem which spans both Class 1 & Class 3? [I cannot find any position which can end in Class 1 & Class 3, without admitting the possibility of a stalemate. So I can't even begin to apply A1.3. This one may be insoluble.] (12) Is there a position which is illegal for both White and Black to play for DR reasons, which is not Class 3? [It is conjectured no such position can exist.Under Class 3 #040 and closely related positions are mutually illegal.] (13) What is the minimum number of pieces required to exhibit a certain last move? For example for Type B Last Moves, 4 units was thought to be the record to force KxN. However, #043 proves that it can be done with 3 units. [See Retro Corner Glossary, "Last move?" for details. (14) Ceriani-Frolkin theme (promotion to specific piece which then is captured). A simple position with 7 units, #055, has been found that exhibits the theme. The promoted piece is captured also in the line following the key sub. (15) Forward play. We have not given much attention to problems with interesting forward play (although we have stumbled across a couple of nice examples.) What great forward affects can be achieved in A1.3 problems, not necessarily using A1.3, but despite the constraints which A1.3 gives. (16) Retro play. We have deliberately avoided trying to create huge retro problems. The state of the art is beyond me, and also there was the concern that the DR theme might be diluted if mixed in with a mass of retro logic. We think there is nevertheless an opportunity to create interesting retro problems, despite the constraints which A1.3 brings. (17) True last move. Is there a problem where the caption is "Last move?" and A1.3 applies to both the cases White to move and Black to move. (In one case, the position is illegal, and the other, the position is restricted.) All problems to date which are "Last move?" use A1.3 only on one side. (18) Take challenge number 2, but relax it so the position does not have to be DR restricted What is the minimum number of pieces necessary to force the legality or an illegality of an en passant or Black/White castling under these circumstances? (19) Caption is: "White to move. Stalemate?" DR must make the difference. Easy case: try for minimum number of units, not DR restricted. Hard case: insist is DR restricted.