mekso quaternary operator: polygamma function; for input X1, X, outputs the (-X2)th derivative of Log(ne'o'a(X1, X)) with respect to X1.
By default, X2 = -1 (notice the double-negative). Inherits the defaults for/of "ne'o'a" (for: X3 = ne'o'a2, and X4 = ne'o'a3). The 0th derivative is the identity operator; in order to be consistent with "salri", negative-integer-order derivatives (meaning: positive X2) are antiderivatives. X2 being other than a non-positive integer, or X1 being non-real, should require mention or assumption of the cultural default interpretation of the definition of the differintegral operator. "Log" here denotes the primary branch of the natural (base-e) logarithm. This is a shift of the polygamma function by 1, so as to be consistent with "ne'o". Therefore, the basic digamma function (derived from the gamma, not Pi, function), often denoted "psi0 (z), is equal to this word's output for X1 = z - 1, X2 = -1, X3 = 0, X4 = +infty (notice the prevalence of the default parameter values).