Let A be a unital associative algebra. In its most general form, the parameter-dependent Yang–Baxter equation is an equation for R ( u , u ′ ) , a parameter-dependent element of the tensor product A ⊗ ⊗ A (here, u and u ′ are the parameters, which usually range over the real numbers ℝ in the case of an additive parameter, or over positive real numbers ℝ in the case of a multiplicative parameter).