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 Moors were people of Arab and Berber origins that invaded Spain in 711 AD. By that time the Visigothic kingdom had reached its decline with internal disputes, disease and famine plaguing the entire country. This provided a good opportunity to the Moors to make their way into Spain.