Deleuze writes that: “Thunderbolts explode between different intensities, but they are preceded by an invisible, imperceptible dark precursor, which determines their path in advance but in reverse, as though intagliated. Likewise, every system contains its dark precursor which ensures the communication of peripheral series. As we shall see, given the variety among systems, this role is fulfilled by quite diverse determinations. The question is to know in any given case how the precursor fulfils this role” (Deleuze 2004, 145–46)