1. A characterization of regularly almost periodic minimal flows,;J. Egawa;Proc. Japan Acad. Ser. A,1995
2. Recurrence in Ergodic Theory and Combinatorial Number Theory,;H. Furstenberg;Princeton University Press,1981
3. Almost periodic points with respect to transformation semi-groups,;W. H. Gottschalk;Annals of Math.,1946
4. A survey of minimal sets,;W. H. Gottschalk;Ann. Inst. Fourier,1964
5. Topological Dynamics,;W. H. Gottschalk;Amer. Math. Soc. Coll. Publ.,1955