THE UNTRANSFORM undo the map — f then f-inverse returns the cell

To untransform is to apply the inverse of the map that transformed a cell: the transform doubled the core to 8; the untransform halves it back to 4. When a function is invertible, transform-then-untransform is the identity — the cell returns exactly to where it began. This is the logic of reversible computing: an operation you can run backwards, losing nothing. It is the mirror of dart 332 across the palindrome — the coming-out map that undoes the going-in map — and a small proof that the batch's value-changes, like its place-changes and its masks, all leave a way back to the original cell.