mekso quaternary operator: polygamma function; for input X_{1, X}, outputs the (-X_{2)}th derivative of Log(ne'o'a(X_{1, X})) with respect to X_{1}.

By default, X_{2 }= -1 (notice the double-negative). Inherits the defaults for/of "ne'o'a" (for: X_{3 }= ne'o'a_{2}, and X_{4 }= ne'o'a_{3}). The 0th derivative is the identity operator; in order to be consistent with "salri", negative-integer-order derivatives (meaning: positive X_{2}) are antiderivatives. X_{2} being other than a non-positive integer, or X_{1} 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 "psi_{0 (z)}, is equal to this word's output for X_{1 }= z - 1, X_{2 }= -1, X_{3 }= 0, X_{4 }= +infty (notice the prevalence of the default parameter values).