The construction of examples of self-parallel curves from a closed central curve given by F. J. Craveiro de Carvalho and S. A. Robertson is extended to general dosed regular curves without the assumption of non-vanishing curvature made there. Furthermore, every self-parallel curve in 3-space is shown to be of the type obtained by this construction, if the order of the selfparallel group is greater than 2. These considerations are used to present examples for transnormal curves in 4-space with arbitrarily high degree of transnormality, disproving a longstanding conjecture of M. C. Irwin.The notion of parallel immersions into Euclidean space has been introduced by Farran and Robertson [3]. In particular, self-parallel immersions are generalizations of the so-called transnormal submanifolds which have been studied in several papers (see the survey [5]). In the latter case very detailed results have been obtained for closed curves.The aim of this note is to study parallelism and self-parallelism for curves in Euclidean space, complementing results obtained by Craveiro de Carvalho and Robertson [1]. The more geometric interpretation of the parallelism of immersions introduced in [7] or I-8] is shown to give a better insight into the structure of self-parallel curves. The construction of examples given in [1] will be extended to the general case without the restriction on the curvature needed there. Furthermore, every self-parallel curve can be obtained in this way from a suitable central curve. Relations between the geometrical data of this central curve and those of the original curve will be obtained.Returning to the case of transnormal curves, these considerations yield a new possibility for the construction of transnormal curves. This is used to show that there are transnormal curves in E 4 of an arbitrarily high degree of transnormality, solving an old problem posed by Irwin [4]. Also injective infinitely transnormal immersions of the real line into E 4 are possible, while this can be excluded in E 3.
PRELIMINARIESLet c: D ~ E" be a regular parametrized curve of sufficiently high differentiability in Euclidean n-space, D = R or S 1. As usual let s denote the arc length of e, T(s) its unit tangent field, ~ its (first) curvature and v(t) = N(t) + e(t) the affine normal space of c at t, where N(t) denotes the normal vector space of c at t.