DD1 · 2026-10-21

DD1: Undo Did Not Mean Start Again

Undoing the latest move returns to the previous state, not necessarily the start. Track a counter’s positions to see the distinction.

Begin a paper puzzle with a counter at 2. Move it to 5, then to 7. A card says “undo the last move”.

Ravi sends the counter straight back to 2. His friend points to the word “last”. Only the move from 5 to 7 should be reversed.

Undo one recorded action at a time

After one undo, the position is 5. After another undo, it returns to 2. Two recorded moves require two reversals to recover the start.

A reset instruction would return to the starting arrangement directly. It is a different command even when both procedures eventually reach the same place.

Write each old position before moving. Without a history, the current square alone may not identify where the counter came from.

Now use the route 2, 5, 2. The final position equals the start, but the last move still came from 5.

The same position can occur twice

Undoing that last move returns to 5, not to a blank history. Equal positions can occur at different moments in a sequence.

Keep any score rule separate from the movement rule. A classroom puzzle may restore position without specifying whether a score is restored.

Let a partner read the history backwards while you move the counter. Stop after the requested number of reversals.

Ravi now distinguishes three questions: where am I, where was I last, and where did I begin? His next undo follows the middle question.

DD1: Undo Did Not Mean Start Again

Undo one recorded action at a time

The same position can occur twice

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