Approximation Theorems Connected with Generalized Translations. J. PEETRE; J. LÖFSTRÖM — 1969 Mathematische Annalen
Convergence analysis of finite difference schemes for semi-linear initial-value problems J. Löfström; V. Thomée — 1976 ESAIM: Mathematical Modelling and Numerical Analysis - Modélisation Mathématique et Analyse Numérique