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# writhe

*writhe* of a link, also called its *twist number*, is
the sum of the signs of the link’s crossings. In short, it is the sum of the positive crossings minus the sum of the negative crossings. Note that the writhe is not an isotopy invariant and that is actually depends on the regular homotopy class of its projection.

Synonym:

twist number

Major Section:

Reference

Type of Math Object:

Definition

Parent:

## Mathematics Subject Classification

57M25*no label found*

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