Figure-eight knot 2026-09-28
The figure-eight knot is the unique knot of crossing number of a knot four. It is prime, alternating, and has Alexander polynomial of a knot up to a unit.
Take the twist knot whose standard diagram has half-twists in its twist region and two crossings in its clasp. Every nontrivial twist knot has Seifert genus one. This diagram is a reduced alternating knot diagram, so the Tait crossing-number theorem says that its crossings realize the crossing number of a knot. Thus this knot has and .
Trefoil knot 2026-09-28
The trefoil is the torus knot . It has Seifert genus one, crossing number of a knot three, and Alexander polynomial of a knot up to a unit.