@article {SC.4.Cascarval.2004,
	title = {Spectral Analysis of Darboux Transformations for the Focusing NLS Hierarchy},
	journal = {Journal d{\textquoteright}Analyse Mathematique},
	volume = {93},
	year = {2004},
	pages = {139-198},
	author = {R. C. {Cascarval} and Gesztesy, F. and Holden, H. and Latushkin, Y.}
}
