Ⅰ．Definitions and preliminary discussions 1
1．Definitions of cluster sets 1
2．Some classical theorems 3
Ⅱ．Single-valued analytic functions in general domains 5
1．Compact set of capacity zero and Evans-Selberg＇s theorem 6
2．Meromorphic functions with a compact set of essential singularities of capacity zero 9
3．Extension of Iversen＇s theorem on asymptotic values 14
4．Extension of Iversen-Gross-Seidel-Beurling＇s theorem 15
5．Hervé＇s theorems 26
Ⅲ．Functions meromorphic in the unit circle 32
1．Functions of class (U) in Seidel＇s sense 32
2．Boundary theorems of COLLINGWOOD and CARTWRIGHT 48
3．Baire category and cluster sets 57
4．Boundary behaviour of meromorphic functions 70
5．Meromorphic functions of bounded type and normal meromorphic functions 81
Ⅳ．Conformal mapping of Riemann surfaces 90
1．Gross＇ property of covering surfaces 90
2．Iversen＇s property of covering surfaces 95
3．Boundary theorems on open Riemann surfaces 98
Appendix:Cluster sets of pseudo-analytic functions 109
Bibliography 121
Subject Index 133