Enumerability · Decidability Computability (2nd ed.)

Once we have accepted a precise replacement of the concept of algo­ rithm, it becomes possible to attempt the problem whether there exist well-defined collections of problems which cannot be handled by algo­ rithms, and if that is the case, to give concrete cases of this kind. Many such investigations were carried out during the last few decades. The undecidability of arithmetic and other mathematical theories was shown, further the unsolvability of the word problem of group theory. Many mathema