6. On Amphicheiral Forms and their Relations
Tait · Proceedings of the Royal Society of Edinburgh · 1878
If a cord be knotted, any number of times, according to the pattern below it is obviously perverted by simple inversion. Hence, when the free ends are joined it is an amphicheiral knot. Its simplest form is that of 4-fold knottiness. All its forms have knottiness expressible as 4n.