The Butterfly lemma. (February 2022) - Castillo, Jesús M.F.
Abstract: The Butterfly lemma we present can be considered a reiteration theorem for differentials generated from a complex interpolation process for families of Köthe spaces. The lemma will be used to clarify the effect of different configurations in the resulting differential (because although interpolation is an orientation-free process, the obtention of differentials is not) and to round off a few aspects of Kalton's interpolation theorem.