"ln(x)" is another way of writing log sub e of x https://en.m.wikipedia.org/wiki/Natural_logarithm

The "ln" of the "you son of a bitch. I'm ln" is referencing that identity

ln(x) (I believe abbreviated from the french logarithme naturel) is the same as the logarithm of x base e (loge(y))

Edit: subscript doesn't seem to work for me on Jerboa but I'm keeping it as it is

ln you a hand