Ln

\(\ln \!=\!\log_{\mathrm e}\!=\!\mathrm{Log}\) is name of natural logarithmic function, that appears as solution of the differential equation

\(\displaystyle \ln'(z)=\frac{1}{z}\)

or as inverse function, id est, the minus first iteration of natural exponential exp,

\(\ln(z)=\exp^{-1}(z)\)