Bowline draws tighter as tension is placed on the standing part of the rope. The "Birmingham bowline" has two loops; the working part is passed twice around the standing part (the "rabbit" makes two trips out of the hole and around the tree). Other two-loop bowline knots include the Spanish bowline and the bowline on the bight; these can be tied in the middle of a rope without access to the ends. A triple bowline is used to make three loops. A Cossack knot is a bowline where the running end goes around the loop-start rather than the main part and
Signature of a knot Signature of a knot The signature of a knot is a topological invariant in knot theory. It may be computed from the Seifert surface. Given a knot "K" in the 3-sphere, it has a Seifert surface "S" whose boundary is "K". The Seifert form of "S" is the pairing formula_1 given by taking the linking number formula_2 where formula_3 and formula_4 indicate the translates of "a" and "b" respectively in the positive and negative directions of the normal bundle to "S". Given a basis formula_5 for formula_6 (where "g" is the genus of the surface) the Seifert form can be