*Augsburg Chess* is a fairy condition in which it is legal
to move a unit to a square already occupied by a unit **of the
same color**.

This results in a combined unit which shares the power of the two units. This combined unit can be moved "normally". It can also be split back into two components when you move one component and let the other one still on the from-square. In the end, every unit is a summation of several individual "atomic" units.

Beyond these general principles, the first point you need to understand
is that, in Augsburg chess, "Queens" do not exist any more. They are
Rook + Bishop combinations. So that a game may start **1. e2-e4
d7-d5 2. Bd1-h5 Rd8-d6** leaving a white Rd1 and a black Bd8!

Other, less important, details are:

- Kings do not combine.
- Equal units can combine and then split. After 1. Ra1-b1 .. 2. R+Nb1-c1 .. 3. R+N+Bc1-d1 you have two Rs and two Bs (and one N) on d1.
- A part-Pawn unit reaching 8th rank has its Pawn-part promoted into N, B, R, or "Q", or in a combined unit which is on the board at the moment of promotion.
- If a part-Pawn unit makes a Pawn double-step, the Pawn-part can be captured en passant by a Pawn (or any unit with a Pawn-part)
- Castling with a combined unit (on a1 or h1) is allowed, if it has a Rook-part which has not moved. The combined unit may only castle with all components, with only the Rook-part, or with a 'queen' part.
- A part-Pawn unit may reach the 1st rank.
- A part-Pawn unit on the 1st rank can move one square forward (or capture on diagonal square).

I don't have a nice pedagogical example of how Augsburg chess gives
rise to fun retros (send me one). There exist some variants of these
rules but most problems (including
number *6556* from feenschach,
Nov 1993, the real motivation for this page) can be solved without
this knowledge. I'll update this page when I can find some more information.

(In the meantime, thanks to Bernd Schwarzkopf for posting the above rules, and thanks to Juraj Lörinc for answering some questions)