Related to the question of solvability or unsolvability of problems is that of the reducibility or non-reducibility of one problem to another. Thus, if problem \(P_1\) has been reduced to problem \(P_2\), a solution of \(P_2\) immediately yields a solution of \(P_1\), while if \(P_1\) is proved to be unsolvable, \(P_2\) must also be unsolvable. For unsolvable problems the concept of reducibility leads to the concept of degree of unsolvability, two unsolvable problems being of the same degree of