mekso (no-more-than-4-ary) operator: Gaussian function f(x, a, b, c) = c e^{-((x-a)}.

Parameter 'a' is the SECOND operand; x is the first. Defaults: c = 1/ \sqrt2 \pi \sigma (normalized), a = \mu (the arithmetic average of the data set), b = \sigma (the standard deviation of the data set). Moreover, by context, \mu = 0 (the average is 0) or \sigma = 1 (the standard deviation is 1) might be assumed by default.