Bridge number

In a mathematical field of Knot theory, the Bridge number is an invariant of a knot. It is defined as the minimal number of bridges required in all the possible bridge representations of a knot. A bridge representation of a knot is a representation, such that the knot lies entirely in the plane apart for a couple of bridges whose projections onto the plane are straight lines.

It can be shown that every n-bridge knot can be decomposed into two trivial n-tangles and hence 2-bridge knots are rational knots.

ources

Peter Cromwell, "Knots and Links", Cambridge

Other invariants

* Linking coefficient
* Unknotting number
* Polygonal number

ee also

* 2-bridge knot