One key's count as its arrivals stop — what is true, and what each structure says

One key's count as its arrivals stop — what is true, and what each structure says

Key 1 takes about a third of the first half of the stream and never appears again. The solid line is its true count in the last 4,096 arrivals, computed by a referee that keeps everything; the others are what each structure reports when asked. The exact windowed structure follows the truth because it is the truth. The blocked summary follows it down with a lag of one block — 512 arrivals — which is the slack its accounting already declares. The clockless Misra-Gries does not come down at all: its counter is not a record of arrivals, it is a number that has been added to and decremented, and there is no operation that removes the contribution of an arrival that has left. It ends at 6,493 against a true 0.

Drawn at 700 × 430, wide on the page. Everything above is what departure returns with no arguments; the caption is the generator's own, computed from the numbers in the drawing rather than written beside it.

1 essay calls departure. The drawing above is what it returns with no arguments at all; every call below passes it something, because a placement that passes nothing draws whichever member of the family the generator happens to default to rather than the one its essay argues about — which is what optcheck and figfill exist to catch.