 Moreover, all the words "w""j" represent the same element of "G" as does "w" and hence if the process terminates with the empty word, then "w" represents the identity element of "G".One says that for a symmetrized presentation (∗) "Dehn's algorithm solves the word problem in" "G" if the converse is also true, that is if for any freely reduced word "w" in "F"("X") this word represents the identity element of "G" if and only if Dehn's algorithm, starting from "w", terminates in the empty word.Greendlinger's lemma implies that for a C'(1/6) presentation Dehn's algorithm solves the word problem.