In 1974 Perko discovered a duplication in the Tait-Little tables, called the Perko pair.
Trefoil knot | knot | 7₄ knot | Turk's head knot | Cinquefoil knot | Rustic Shoulder-knot | Knot's Landing | Constrictor knot | Celtic knot | True lover's knot | The logo of the Ontario Crafts Council, designed by Debbie Adams of Adams + Associates Design Consultants. Knot symbol designed by Burton Kramer | The ''epankylotos brokhos'' or the modern Tom fool's knot | Slip knot | root-knot nematode | Reef knot | Red Knot | red knot | Overhand knot | Knot (unit) | Knot | Hungerford knot | Gordian Knot | Blood Knot | Bight (knot) |