The {{CMD_144}} of {{MATH_145}} at {{MATH_146}}, denoted {{MATH_147}}, is given by {{MATH_148}} provided that the limit exists. We say that {{MATH_149}} is {{CMD_150}} at {{MATH_151}} if this limit exists. Otherwise, we say that {{MATH_152}} is {{CMD_153}} at {{MATH_154}}. {{CMD_155}}