#5: the edge eating into the block, steps 0 to 10⁹, one row every 400,000 steps

blank: row 0 = step 0

every 400,000 steps: 2,501 rows for steps 0..1e9, 1 px tall each

between two rows the head makes 506 round trips (first rows) down to 6 (last rows): each row is a snapshot, so row-to-row jumps sum many bounces

cells −349..2,250, 1 px = 1 cell: the left 2,600 cells of the 32,607-cell tape at 1e9

1   0 or never visited   head (last move right / left)

bbchallenge default colors; blue numbered dots are annotations