Characterizations of the sphere in E 4 by means of the pseudoparallel mean curvature vector field Karel Svoboda (1980) Časopis pro pěstování matematiky Similarity:
Determination of a surface by its mean curvature Alois Švec (1978) Časopis pro pěstování matematiky Similarity:
Several new characterizations of the 2-dimensional sphere in E 4 Karel Svoboda (1979) Czechoslovak Mathematical Journal Similarity: