1. Casson, A.: Link cobordism and Milnor's invariant. Bull. Lond. Math. Soc.7, 39?40 (1975)
2. Cochran, T.D.: Geometric invariants of link cobordism. Comment.60, 291?311 (1985)
3. Cochran, T.D.: Derivatives of links: Milnor's concordance invariants and Massey's products. University of California, San Diego 1985 (Preprint)
4. Conway, J.H.: An enumeration of knots and links and some of their algebraic properties. In: Computational Problems in Abstract Algebra John Leech, (ed.), pp. 329?358. Oxford-New York: Pergammon Press 1970
5. Fox, R.H., Milnor, J.W.: Singularities of 2-spheres in 4-space and cobordism of knots. Osaka J. Math.3, 257?267 (1966)