 In view of this, Cross introduces a contextual parameter in his account of how-questions to indicate whether a given how-question presupposes that all members of the contrast class are true or whether it presupposes that all members of the contrast class other than \(P\) are false. In the resulting account, a how-question is an ordered quadruple \(\langle P,X,R,n\rangle\), where \(P\) is the topic of the question; \(X\) is the contrast class, which is a set of propositions to which \(P\) belongs; \(R\) is a contextually determined relation of explanatory relevance, which holds between a proposition and the topic/contrast-class pair \(\langle P,X\rangle\), and \(n\) is the contrast value 0 or 1. If \(n = 0\), the question presupposes that in \(X\) only \(P\) is true; if \(n = 1\), the question presupposes that all of the members of \(X\) are true. The explanatory relevance relation \(R\) is to be understood as varying from context to context depending on what kind of way is being requested in that context. Finally, Cross (1991, 252) defines a direct answer to a how-question as follows: