 Suppose that \(H\) together with another set of hypotheses \(H'\) (and some auxiliaries A) entail a prediction \(P\). \(H\) indispensably contributes to the generation of \(P\) if \(H'\) and A alone cannot yield \(P\) and no other available hypothesis \(H^*\) which is consistent with \(H'\) and A can replace \(H\) without loss in the relevant derivation of \(P\). 