Cesàro's theorem is a subtle example. The series 1 − 1 + 1 − 1 + ... is Cesàro-summable in the weakest sense, called (C, 1)-summable, while 1 − 2 + 3 − 4 + ... requires a stronger form of Cesàro's theorem,[8] being (C, 2)-summable. Since all forms of Cesàro's theorem are linear and stable, the values of the sums are as we have calculated.