Butzer Paul L. & Berens, H. (1967). Semi-groups of operators and approximation.
Chicago Edition CitationButzer Paul L. and Hubert Berens. Semi-groups of Operators and Approximation. 1967.
MLA Edition CitationButzer Paul L. and Hubert Berens. Semi-groups of Operators and Approximation. 1967.
Warning: These citations may not always be 100% accurate.