 If a C'(1/6) presentation (∗) is finite (that is both "X" and "R" are finite), then Dehn's algorithm is an actual non-deterministic algorithm in the sense of recursion theory.However, even if (∗) is an infinite C'(1/6) presentation, Dehn's algorithm, understood as an abstract procedure, still correctly decides whether or not a word in the generators "X"±1 represents the identity element of "G".Let (∗) be a C'(1/6) or, more generally, C(6) presentation where every "r" ∈ "R" is not a proper power in "F"("X") then "G" is aspherical in the following sense.