A knot equivalent to a polygon in 
, also called a tame
knot. For a polygonal knot 
, there exists a plane such that
the orthogonal projection 
on it satisfies the following conditions:
1. The image 
has no multiple points other than a finite number of double
points.
2. The projections of the vertices of 
are not double points of 
.
Such a projection 
is called a regular knot projection.
