  In quantum field theory with a mass gap correlation function between two
spatially separated operators decays exponentially with the distance. This
fundamental result immediately implies an exponential suppression of all higher
point correlation functions, but the predicted exponent is not optimal. We
argue that in a general quantum field theory the optimal suppression of a
three-point function is determined by total distance from the operator
locations to the Fermat-Steiner point. Similarly, for the higher point
functions we conjecture the optimal exponent is determined by the solution of
the Euclidean Steiner tree problem. We discuss how our results constrain
operator spreading in relativistic theories.
