The funnel at 3 errors: 20,000 positions to 7 answers

The funnel at 3 errors: 20,000 positions to 7 answers

A pattern of 24 characters over four symbols, allowed 3 errors. The index proposes 140 starting positions out of 20,000; each is verified by a banded table of at most 24x30 cells; 7 survive. The whole thing computes 28,700 table cells against the 480,000 of filling the rectangle over the whole text — a factor of 16.7. The selectivity, which is the only number that says whether the filter was worth running, is 5.0%.

Drawn at 700 × 218, wide on the page. Everything above is what filter-funnel returns with no arguments; the caption is the generator's own, computed from the numbers in the drawing rather than written beside it.

3 essays call filter-funnel. 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.