Ioannis Galidakis, Mathematics, (Definitive list of references to tetration research. Lots of information on the Lambert W function, Riemann surfaces, and analytic continuation.)
Galidakis, Ioannis and Weisstein, Eric W. Power Tower
Hans Maurer, "Über die Funktion y = x [ x [ x ( ⋯ ) ] ] {\displaystyle y=x^{[x^{[x(\cdots )]}]}} für ganzzahliges Argument (Abundanzen)." Mittheilungen der Mathematische Gesellschaft in Hamburg 4, (1901), p. 33–50. (Reference to usage of n a {\displaystyle \ {^{n}a}} from Knobel's paper.)
