unary mekso operator: Lorentz-Einstein gamma factor +1/((1-(|X|2)) for input X.
Typically, input X can be a scalar (typically between -1 and 1, exclusive of both endpoints except in the limit) or a vector (or a similar mathematical object) with a signed magnitude belonging to the previously mentioned interval; in the former case, "|X|" in the definition refers to its absolute value; in the latter case, "|X|" in the definition refers to the nonnegative magnitude of said vector (or similar object). Typically, the output is a(n extended) real number no less than 1; whether or not positive-infinity exists in the codomain is a matter of convenience, convention, and context. This definition can be extended (such as for tachyons).