 On the one hand, any cluster, for example \(C_1 \land C_2\), is minimally sufficient for \(E\) (and so is the “cluster” \(D_1\)). \(C_1 \land C_2\) is minimally sufficient for \(E\) means that the cluster is sufficient for \(E\) and each conjunct of the cluster is necessary for its sufficiency. So no conjunct of any cluster is redundant for bringing about the effect. On the other hand, neither cluster is necessary for the effect \(E\). \(C_1 \land C_2\) is minimally sufficient but not necessary for \(E\). \(E\) occurs if \(D_1\) does. Now, focus on \(C_1\) which is on its own insufficient to bring about \(E\). \(C_1\) is a single factor of the cluster \(C_1 \land C_2\) which is a sufficient but unnecessary condition for \(E\). Hence, \(C_1\) is an insufficient but non-redundant part of an unnecessary but sufficient condition for \(E\) (relative to a causal field). Or simply, \(C_1\) is an INUS condition for \(E\).