On the existence and characterization of minimal projections. P.D. Morris; E.W. Cheney — 1974 Journal für die reine und angewandte Mathematik
Continuity of the Set-valued Metric Projection. J. BLATTER; P.D. MORRIS; D.E. WULBERT — 1968 Mathematische Annalen
Chebychev Sets which are not Suns. B. Brosowski; F. Deutsch; J. Lambert; P.D. Morris — 1974 Mathematische Annalen