Graph index: the build, one place at a time

Build Before each step, say which places the new one keeps, and whether any list overflows.

Level shown

On the map: a plain line links two places that list each other; an arrow, a link only one end lists, pointing at the place listed. Heavy: the new place's links. Dotted, with a number: a skipped candidate and the pick nearer to it. Dashed with a red head: a link taken off a list.