H. G. Muller wrote on Mon, Apr 18, 2022 08:58 AM UTC:
A somewhat simplified version of the same idea is this:
h5
a4
There is only a single, double-width cell a4 here,
and there is no additional game state to distinguish between an occupant being in the right or left half of it.
Moves (or move continuations) that leave a4 to 5th rank can choose whether they consider a5 or b5 the only square that connects to the upper edge of a4. So a4 has 2 'north' exits (to a5 and b5), two 'north-east' exits (to b5 and c5), and a single 'north-west' exit (to a5).
The difference with the rules that were given is that 'forward' moves even fork from a4, in addition to a1-a3.
How a Knight should move in the vicinity of the switch fields depends on which of the (normally equivalent) descriptions of Knight moves one adopts for the regular part of the board.
The description "all two-step King moves that cannot be made by a Queen" is a rather unusual one;
commonly one finds "one orthogonal King step followed by an outward diagonal one" (i.e. a non-lame Mao) or L-shaped "2 orthogonal steps plus a perpendicular one". Where the latter might also allow the move to start with the short leg.
In my opinion the non-lame Mao description would be most intuitive here.
A somewhat simplified version of the same idea is this:
There is only a single, double-width cell a4 here, and there is no additional game state to distinguish between an occupant being in the right or left half of it. Moves (or move continuations) that leave a4 to 5th rank can choose whether they consider a5 or b5 the only square that connects to the upper edge of a4. So a4 has 2 'north' exits (to a5 and b5), two 'north-east' exits (to b5 and c5), and a single 'north-west' exit (to a5).
The difference with the rules that were given is that 'forward' moves even fork from a4, in addition to a1-a3.
How a Knight should move in the vicinity of the switch fields depends on which of the (normally equivalent) descriptions of Knight moves one adopts for the regular part of the board. The description "all two-step King moves that cannot be made by a Queen" is a rather unusual one; commonly one finds "one orthogonal King step followed by an outward diagonal one" (i.e. a non-lame Mao) or L-shaped "2 orthogonal steps plus a perpendicular one". Where the latter might also allow the move to start with the short leg. In my opinion the non-lame Mao description would be most intuitive here.