see also Sect. 7.1 pg(s). 121-128 in "J. Komara and P. J. Voda. Lecture Notes in Theory of Computability. 2001."
see also Sect. 7.2 pg(s). 129-138 in "J. Komara and P. J. Voda. Lecture Notes in Theory of Computability. 2001."