Mainspring

A programming duel for two — the shelf’s only one. A three-by-six workshop floor with a vise bolted shut at c2; two clockwork couriers, Ivory bound right and Coral bound left. Each round both houses WIND three gears in secret (up, down, left or right each); the springs then run down in public, houses alternating one step at a time. Which spring runs down first is drawn when they are let go, and the board says whose it is before the winding. A step into the wall or the vise burns the gear; a step into the rival PUSHES them one square your way and you follow — and a shove onto their own bench delivers for THEM. Reaching your far column wins mid-march; nobody can deliver together, so there is no draw, ever, said plainly.

How it feels

• Reading the march the rival could not hide
• A shove that lands them off their lane
• Three gears that walk it home in one wind

What the design is for

• 01

  Wound in secret, run in the open

  Three gears each, committed blind, then six public steps — the whole game is writing a march you can defend against every march the rival might have wound. The engine hides the rival’s gears until the springs run; a test proves it.

• 02

  The shove

  The rival’s square is not a wall: stepping in pushes them one square your way and you follow. Shoves clear lanes, waste rivals’ gears, and — priced honestly — can push a courier onto its own bench to hand over the game.

• 03

  The vise at the centre

  One cell of the floor is a fixed vise: no march crosses the middle lane, no courier stands there, and no mirror survives it. The detour you plan around the vise is most of the craft.

• 04

  No draw, ever

  One courier steps at a time, so only one can deliver in a round — and if the springs wear out after twelve winds, the nearer courier is judged the delivery, an exact stand-off judged against the march’s lead. Somebody always wins, said plainly. Between two couriers that walk straight at each other it is the wear-out that decides: the probe’s two walkers jammed in the middle lane and ran the springs out in 150 matches of 150, six shoves in the last march of every one.

• 05

  The lead is drawn, not taken

  The lead of the march used to alternate by round, and that made the game solved: a race of equal length is won by whoever steps first in the round it ends, so the winner was a function of the round number. Every strong opponent against every other strong opponent measured exactly 75–75 over a hundred and fifty matches, each winning precisely the matches it was seated for. The lead now comes off the match’s own seed, public before the winding, and replays exactly.

• 06

  Taught gear by gear

  Six steps: the winding, the march home, the burning wall and the vise, the shove, the gift shove to avoid — and then a whole floor to yourself. Every square is named the way the board names it now; four of the steps used to call the top row 1 where the board prints 3, and two asked the player to wind up out of the top row into the wall the step before had taught them never to touch.