Stépéni Nérazréšimosti Problémy Toždéstva v Konéčno Oprédélénnyh Gruppah.by A. A. Friedman;Degrees of Insolvability of the Word Problem in Finitely Defined Groupby A. A. Fridman; Sue Ann Walker;Finitely presented Groups with Word Problems of Arbitrary Degrees of Insolubilityby C. R. J. Clapham;Finitely Presented Group Whose Word Problem has the Same Degree as that of an Arbitrarily Given Thue System (An Application of Methods of Britton)by William W. Boone;Word problems and Recursively Enumerable Degrees of Unsolvability. A First Paper on Thue Systemsby William W. Boone;Word Problems and Recursively Enumerable Degrees of Unsolvability. A Sequel on Finitely Presented Groupsby William W. Boone