The Existence and Unicity of Best Approximations. E.W. Cheney; D.E. Wulbert — 1969 Mathematica Scandinavica
Corrigendum to "The Existence and Unicity of Best Approximations". E.W. Cheney; D.E. Wulbert — 1970 Mathematica Scandinavica
Continuity of the Set-valued Metric Projection. J. BLATTER; P.D. MORRIS; D.E. WULBERT — 1968 Mathematische Annalen