1. George K. Francis, The folded ribbon theorem, Dissertation, Univ. of Michigan, 1967. (University Microfilms Abstract 67-15,622, Vol. 28,6, 1967.)
2. Über die Drehung der Tangenten und Sehnen ebener Kurven;Hopf, Heinz;Compositio Math.,1935
3. Morris L. Marx and Roger F. Verhey, Polynomial extensions of normal curves, (to appear).
4. Lectures on the H-Cobordism Theorem
5. On regular homotopy in codimension 1;Poenaru, Valentin;Ann. of Math. (2),1966