Every isometric immersion of ${\boldsymbol R}^2$ into ${\boldsymbol R}^4$ with
vanishing normal curvature is assosiated with a pair of real-valued functions
satisfying a system of second order partial differential equations of hyperbolic
type,and vice versa. An isometric immersion with vanishing normal curvature is
revealed to be multiple-valued in general as is shown by some concrete
examples.
@article{1264084498,
author = {Mori, Hiroshi and Shimakura, Norio},
title = {Isometric immersions of Euclidean plane into Euclidean 4-space with vanishing
normal curvature},
journal = {Tohoku Math. J. (2)},
volume = {61},
number = {1},
year = {2009},
pages = { 523-550},
language = {en},
url = {http://dml.mathdoc.fr/item/1264084498}
}
Mori, Hiroshi; Shimakura, Norio. Isometric immersions of Euclidean plane into Euclidean 4-space with vanishing
normal curvature. Tohoku Math. J. (2), Tome 61 (2009) no. 1, pp. 523-550. http://gdmltest.u-ga.fr/item/1264084498/