 A probability measure Pr on \(\mathbf{A}\) is regular just in case \(\Pr(A) \gt 0\) for every non-empty or consistent proposition \(A\) in \(\mathbf{A}\). Let \(\mathbf{A}^{\Pr}\) be the set of all propositions \(A\) in \(\mathbf{A}\) with \(\Pr(A) \gt 0\). The conditional probability measure \(\Pr(\cdot\mid -): \mathbf{A}\times \mathbf{A}^{\Pr} \rightarrow \Re\) on \(\mathbf{A}\) (based on the non-conditional probability measure Pr on \(\mathbf{A})\) is defined for all pairs of propositions \(A\) in \(\mathbf{A}\) and \(B\) in \(\mathbf{A}^{\Pr}\) by the ratio