 However, as it stands these results are purely heuristic. The thirty years following Cantor’s publication of his table of values (described by Echeverria as the “2nd period” of research into GC) saw numerous attempts to find an analytic expression for G(n). If this could be done then it would presumably be comparatively straightforward to prove that this analytic function never takes the value 0 (Echeverria 1996, 31). By around 1921, pessimism about the chances of finding such an expression led to a change of emphasis, and mathematicians started directing their attention to trying to find lower bounds for G(n). This too has proved unsuccessful, at least to date.