Based on the present theories of buffer operators, the following results is proved: If d is a weakening buffer operator, ??x(k)d is an expression made up of x(k) ... x(n). f is a strictly monotone function, and g is its inverse function. While d is working on the data sequence, ??f(x(k)) is used to take the place of x(k)d. Then g is used to work on the resulting expression, and the result is noted with e. So if d is weakening buffer operator, e is also a weakening buffer operator.