Granny knot its possible use tying the necks of grain sacks. When attempting to tie a reef knot (square knot), it is easy to produce a granny knot accidentally. This is dangerous because the granny knot can slip when heavily loaded. A tightened granny knot can also jam and is often more difficult to untie than the reef knot. It is better to tie a reef knot in nearly all circumstances. One way to distinguish them is that in the reef knot each loop passes completely over, or completely under (not through) the neck of the other. The reef knot is commonly
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