  However, this derivation utilizes the fact that \(r\) is a  factive justification for \(B\) to conclude  \(w : B \rightarrow B\), which constitutes a case of  ‘induced factivity’ for \(w : B\). The  question is, how can one distinguish the ‘real’ factivity of \(r : B\) from the ‘induced factivity’ of  \(w : B\) ? Some sort of evidence-tracking is needed here,  and Justification Logic is an appropriate tool. The natural approach  is to consider the set of assumptions without  \(r : B\), i.e.,