Apparatus and corresponding methods are disclosed relating to circuitry to perform an arithmetic operation on one or more input operands, where the circuitry is responsive to an equivalence of a result value of the arithmetic operation with at least one of the one or more input operands, when the one or more input operands are not an identity element for the arithmetic operation, to generate a signal indicative of the equivalence. Idempotency (between at least one input operand and the result value) is thus identified.