Schubert (1949) showed that every knot can be uniquely decomposed (up to the order in which the decomposition is performed) as a knot sum of a class of knots known as prime knots, which cannot themselves be further decomposed (Livingston 1993, p. 5; Adams 1994, pp.
The Moors were Muslim inhabitants of the Maghreb, the Iberian Peninsula, Sicily, and Malta during the Middle Ages.
The Sahara's fabled dune fields, which cover only about 15 percent of the entire desert's surface, lie primarily in the north central region, in the countries of Algeria and Libya. Most sand dunes -- mounds and ridges of sand sculpted by wind and gravity -- have a windward or backslope surface and a leeward or slipface surface.