.SH
Acknowledgement
.PP
I am grateful to Ted Dolotta
for his careful reading and valuable suggestions.
.SH
References
.IP [1]
Brian W. Kernighan,
.ul
A Tutorial Introduction to the UNIX Text Editor,
Bell Laboratories internal memorandum.
.IP [2]
Brian W. Kernighan,
.ul
UNIX For Beginners,
Bell Laboratories internal memorandum.
.IP [3]
Ken L. Thompson and Dennis M. Ritchie,
.ul
The UNIX Programmer's Manual.
Bell Laboratories.