Sossinsky:Knots. Mathematics with a twist.pdf - English
Sossinsky:Knots. Mathematics with a twist.pdf - English
Sossinsky:Knots. Mathematics with a twist.pdf - English
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KNOTS<br />
Figure 1.3. Planar projection of a knot.<br />
specifying which knots belong to the same class. It requires, in other<br />
words, precisely defining the equivalence of knots. Sut we will leave this<br />
definition (the ambient isotopy of knots) for later, limiting ourselves<br />
here to an intuitive description. Imagine that the curve defining the<br />
knot is a fine thread, flexible and elastic, that can be <strong>twist</strong>ed and<br />
moved in a continuous way in space (cutting and gluing back is not al<br />
lowed). AlI possible positions will thus be those of the same knot.<br />
Changing the position of the curve that defines a knot in space by<br />
moving it in a continuous way (<strong>with</strong>out ever cutting or retying it) al<br />
ways results in the same knot by definition, but its planar representa<br />
tion may become unrecognizable. In particular, the number of cross<br />
ings may change. Nevertheless, the natural approach to classifying