A function {{MATH_65}} has a {{CMD_66}} at {{MATH_67}}, if {{MATH_68}} for every {{MATH_69}} in some open interval I containing {{MATH_70}}. {{CMD_71}} A function {{MATH_72}} has a {{CMD_73}} at {{MATH_74}}, if {{MATH_75}} for every {{MATH_76}} in some open interval I containing {{MATH_77}}. {{CMD_78}} A {{CMD_79}}{{CMD_80}} is either a local maximum or a local minimum. These are sometimes referred to as {{CMD_81}} as well. {{CMD_82}}