A link invariant defined for a two-component oriented link as the sum of crossings and crossing over all crossings between the two links divided
by 2. For components
and ,

where
is the set of crossings of with , and is the sign of the crossing. The linking number of
a splittable two-component link is always 0.

Kauffman, L. Knots and Physics. Teaneck, NJ: World Scientific, p. 19, 1991.Pohl,
W. F. "The Self-Linking Number of a Closed Space Curve." J. Math.
Mech.17, 975-985, 1968.Rolfsen, D. Knots
and Links. Wilmington, DE: Publish or Perish Press, pp. 132-133, 1976.