Natural extrinsic geometrical symmetries -- an introduction --

摘要

An attempt is made to present the geometrical meanings of the notions of parallel and of semi-parallel and of pseudo-parallel submanifolds, in analogy with the geometrical meanings of the notions of (locally) symmetric and semi-symmetric and pseudo-symmetric manifolds. In a way, the present article may thus be seen as an extrinsic companion of the article "Natural Intrinsic Geometrical Symmetries" in SIGMA's 2009 Special Issue "Elie Cartan and Differential Geometry".