布尔函数
A Boolean function takes the form formula_1, where formula_2 is known as the Boolean domain and formula_3 is a non-negative integer called the arity of the function. In the case where formula_4, the "function" is a constant element of formula_2. A Boolean function with multiple outputs, formula_6 with formula_7 is a "vectorial" or "vector-valued" Boolean function (an S-box in cryptography).