The ''negation'' of a sentence <math>s,\!</math> written as <math>^{\backprime\backprime} \, \underline{(} s \underline{)} \, ^{\prime\prime}</math> and read as <math>^{\backprime\backprime} \, \operatorname{not}\ s \, ^{\prime\prime},</math> is a sentence that is true when <math>s\!</math> is false and false when <math>s\!</math> is true. | The ''negation'' of a sentence <math>s,\!</math> written as <math>^{\backprime\backprime} \, \underline{(} s \underline{)} \, ^{\prime\prime}</math> and read as <math>^{\backprime\backprime} \, \operatorname{not}\ s \, ^{\prime\prime},</math> is a sentence that is true when <math>s\!</math> is false and false when <math>s\!</math> is true. |