User blog comment:B1mb0w/Fundamental Sequences/@comment-27173506-20160207142006

You seem to misunderstand the difference between "the expression is ill defined" and "my function does not cope correctly with the expression". \(\varepsilon_{\zeta_0} = \zeta_0\), by definition. That is a perfectly well defined expression. If you want it more formally, \(\zeta_0 = \text{min} \alpha : \alpha = \varepsilon_{\alpha}\). The fact that your function gives the wrong result is irrelevant. The only thing that it means is that you need to fix your function.