Spanish bowline complicated knot however and if not properly tightened, it can slip. A fireman's chair knot is another double loop knot which is more practical, easier to tie and less prone to slipping although it lacks the elegance of a Spanish bowline. Spanish bowline The Spanish bowline is a double loop knot that can be used to lift a person. For a conscious person, each loop is placed around a leg and the person holds onto the standing part of the rope. This knot can serve as a makeshift Bosun's chair. For an unconscious person one loop is placed around the
Arf invariant of a knot Arf invariant of a knot In the mathematical field of knot theory, the Arf invariant of a knot, named after Cahit Arf, is a knot invariant obtained from a quadratic form associated to a Seifert surface. If "F" is a Seifert surface of a knot, then the homology group H("F", Z/2Z) has a quadratic form whose value is the number of full twists mod 2 in a neighborhood of an imbedded circle representing an element of the homology group. The Arf invariant of this quadratic form is the Arf invariant of the knot. Let formula_1 be a Seifert matrix of