1. Semi-groups of Operators and Approximation;Butzer,1967
2. Singular perturbations for partial differential equations;Friedman;Arch. Rational Mech. Anal.,1968
3. Rate of convergence in singular perturbations;Greenlee;Ann. Inst. Fourier (Grenoble),1968
4. Singular perturbation theorems for semibounded operators;Greenlee;J. Functional Analysis,1971
5. Caractérisation de quelques espaces d'interpolation;Grisvard;Arch. Rational Mech. Anal.,1967