The shah function is defined by ш(x) | congruent | sum_(n = - ∞)^∞ δ(x - n) | congruent | sum_(n = - ∞)^∞ δ(x + n), where δ(x) is the delta function, so ш(x) = 0 for x not element Z (i.e., x is not an integer). The shah function is also called the sampling symbol or replicating symbol, and is implemented in the Wolfram Language as DiracComb[x].