The span of an unoriented link diagram (also called the link spread) is the difference between the highest and lowest degrees of its bracket
polynomial. The span is a topological invariant of a knot. If a knot 
has a reduced alternating projection
of 
crossings, then the span of 
is 
.
Link Span
See also
LinkExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Link Span." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/LinkSpan.html