====Higher Order Propositions and Logical Operators (''n'' = 2)====
====Higher Order Propositions and Logical Operators (''n'' = 2)====
−
By way of reviewing notation and preparing to extend it to higher order universes of discourse, let us first consider the universe of discourse <math>X^\circ = [X] = [x_1, x_2] = [x, y],</math> based on two logical features or boolean variables <math>x\!</math> and <math>y.\!</math>
+
By way of reviewing notation and preparing to extend it to higher order universes of discourse, let us first consider the universe of discourse <math>X^\circ = [\mathcal{X}] = [x_1, x_2] = [x, y],</math> based on two logical features or boolean variables <math>x\!</math> and <math>y.\!</math>