is also a knot (i.e., a link with one component) is a Montesinos knot. A Montesinos link is composed of several rational tangles. One notation for a Montesinos link is . In this notation, and all the and are integers. The Montesinos link given by this notation consists of the sum of the rational tangles given by the integer and the rational tangles These knots and links are named after the Spanish topologist José María Montesinos Amilibia, who first introduced them in 1973. Utility (−2, 3, 2n + 1) pretzel links are especially useful in the study of 3-manifolds. Many results have been stated about the manifolds that result from Dehn surgery on the (−2,3,7) pretzel knot in particular. The hyperbolic volume of the complement of the pretzel link is times Catalan's constant, approximately 3.66. This pretzel link complement is one of two two-cusped hyperbolic manifolds with the minimum possible volume, the other being the complement of the Whitehead link. References Further reading Trotter, Hale F.: Non-invertible knots exist, Topology, 2 (1963), 272–280. 3-manifolds