 \(y +_c x\) expresses the cardinal addition of cardinals y and x. It is the arithmetical sum of “homogeneous cardinals”, cardinals of a uniform type, to which \(\alpha\) and \(\beta\) are related by \(\rN_0 c\) (itself defined at [∗103·01]). The notation indicating that \(\alpha\) is a homogenous cardinal \(\alpha\) is \(\rN_0 c\pmsq\alpha\), which we might write as \(\#_0\) in an extension of our contemporary notation replacing \(\#\) above.