 [‡]    Where \(\mathsf{ab}\) is an abnormal formula in \(\Omega\): if \(\phi\vdash \psi \vee \mathsf{ab}\) then \(\psi\) follows defeasibly from \(\phi\) on the assumption that \(\mathsf{ab}\) is false (or, equivalently, that \(\neg \mathsf{ab}\) is true). 