Convex and starshaped subsets in manifolds product
In [1] the main result (Teorem 2) which States that “a submanifold Mn of a RiemanSian maniforld Mn is an extrinsic sphere (i.e. the submanifold which is umbilic and has parallel mean curvature) iff every circle in Mn is a circle in Mm must have some additional hypothesis. We pointed out these hypothesis just the special case of Mm — IRm
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- Communications, Series A1:Mathematics and Statistics