#### Volume 3, issue 1 (1999)

 1 A Bartels, Link homotopy in codimension two, PhD thesis, UC San Diego (1999) 2 A K Bousfield, D M Kan, Homotopy limits, completions and localizations, Lecture Notes in Mathematics 304, Springer (1972) MR0365573 3 T D Cochran, Link concordance invariants and homotopy theory, Invent. Math. 90 (1987) 635 MR914853 4 S Ferry, Homotoping $\varepsilon$–maps to homeomorphisms, Amer. J. Math. 101 (1979) 567 MR533191 5 M H Freedman, F Quinn, Topology of 4–manifolds, Princeton Mathematical Series 39, Princeton University Press (1990) MR1201584 6 R Fenn, D Rolfsen, Spheres may link homotopically in 4–space, J. London Math. Soc. $(2)$ 34 (1986) 177 MR859159 7 M H Freedman, P Teichner, 4–manifold topology I: Subexponential groups, Invent. Math. 122 (1995) 509 MR1359602 8 M Golubitsky, V Guillemin, Stable mappings and their singularities, Graduate Texts in Mathematics 14, Springer (1973) MR0341518 9 M A Kervaire, J W Milnor, Groups of homotopy spheres I, Ann. of Math. $(2)$ 77 (1963) 504 MR0148075 10 P A Kirk, Link maps in the four sphere, from: "Differential topology (Siegen, 1987)", Lecture Notes in Math. 1350, Springer (1988) 31 MR979332 11 W Massey, D Rolfsen, Problem section, from: "Low-dimensional topology", London Mathematical Society Lecture Note Series 95, Cambridge University Press (1985) MR827295 12 J Milnor, Link groups, Ann. of Math. $(2)$ 59 (1954) 177 MR0071020 13 C P Rourke, Embedded handle theory, concordance and isotopy, from: "Topology of Manifolds (Proc. Inst., Univ. of Georgia, Athens, Ga., 1969)", Markham, Chicago, Ill. (1970) 431 MR0279816 14 J Stallings, Homology and central series of groups, J. Algebra 2 (1965) 170 MR0175956 15 P Teichner, Stratified Morse theory and link homotopy, in preparation 16 P Teichner, Pulling apart 2–spheres in 4–space, preprint (1997)