A link invariant is a function from the set of all links to any other set such that the function does not change as the link is changed (up to isotopy). In other words, a link invariant always assigns the same value to equivalent links (although different knots may have the same link invariant). When the link has a single component and therefore generates to a knot, the invariant is called a knot invariant.

knot | knot invariant | link