He graduated in various disciplines during his life and has taught at several universities .
Van Praag ( co - ) author of several hundred books and articles , and thousands of speeches and lectures , some of which are laid down on tape .
author graduated in various disciplines during author 's life and has taught at several universities .
Van Praag ( co - ) author of several hundred books and articles , and thousands of speeches and lectures , some of which are laid down on tape .