 To illustrate this definition, let us temporarily assume that we know some facts about the natural numbers 1 and 2 to show that the definition properly predicts that \(\mathit{Precedes}(1,2)\), even though we haven’t yet defined these natural numbers. Let the expression ‘\([\lambda z \, Azp]\)’ denote the concept author of Principia Mathematica. Only Bertrand Russell (‘\(r\)’) and Alfred Whitehead fall under this concept. Let the expression ‘\([\lambda z \, Azp \amp z\neqclose r]\)’ denote the concept author of Principia Mathematica other than Russell.[10] Then the following may, for the purposes of this example, be taken as facts: 