Crossing Number

In mathematics, a crossing number is an invariant that gives the minimum number of crossings possible in a drawing, diagram, or projection of a mathematical object, subject to the rules of the setting in question. In knot theory, the knot crossing number or link crossing number is the minimum number of crossings in a knot diagram or link diagram. In graph theory, the unqualified term usually refers to the graph crossing number, while related variants restrict the allowed drawings, edge constructions, or ambient surface.