Csato, G.Dacorogna, B.Kneuss, O.2014-02-172014-02-172014-02-17201410.1007/s00526-012-0593-1https://infoscience.epfl.ch/handle/20.500.14299/100728WOS:000329581200023Let f, g be two closed k-forms over R-n. The pullback equation studies the existence of a diffeomorphism phi : R-n -> R-n such that phi*(g) = f. We prove two types of results. The first one sharpens some of the existing regularity results. The second one discusses the possibility of choosing the map phi as the gradient of a function Phi : R-n -> R. We show that this is a very rare event unless the two forms are constant.text::journal::journal article::research article