“…Loosely speaking, this phenomenon indicates that the fundamental group of a manifold might be not very complicated if is locally isomorphic to such a homogeneous manifold / . The first example for the Calabi-Markus phenomenon was found by Calabi and Markus in 1962 [3] for ( , ) = ( ( , 1), ( − 1,1)), and generalized by Wolf [22] and Kulkarni [15] for ( , ) = ( ( , ), ( ; − 1)) from 1960s to the early 1980s, and then completely settled by Kobayashi [7] in 1989 for reductive Lie groups ( , ) in terms of real rank conditions. The key lemma of Kobayashi's paper [7] is to establish the criterion of proper actions of continuous subgroups.…”