diff --git a/docs/v4.0.0/ENGINE.md b/docs/v4.0.0/ENGINE.md
index 060509a9..8eeba6a2 100644
--- a/docs/v4.0.0/ENGINE.md
+++ b/docs/v4.0.0/ENGINE.md
@@ -304,6 +304,18 @@ Rulings on that step so far:
   other end of a port, in the same table. Nothing in the engine knows
   which geometry is in use. A node is told, or finds out, which port leads
   toward a destination.
+- **What Hera's process management decides (ruled, "A"): which nodes
+  exist and are awake, not whose turn it is.** Every node that is not
+  blocked runs; on one processor that is each in rotation, an instruction
+  word at a time, which is what "all at once" is there and is not a
+  policy. From each node's heat Hera decides which are born, put to sleep,
+  woken and killed (`JUSTIFICATION.md` sections 6 and 7). Cooperative is a
+  node blocking itself at a port; preemptive is Hera putting a node to
+  sleep or killing it between any two instruction words. Nothing in this
+  depends on there being one processor. With it: an idle node does not
+  spin; it is blocked reading its ports and wakes when a neighbour writes,
+  and the console handing it a line is a message arriving on a port like
+  any other.
 - **How it grows: "Only the central node can connect to only another
   central node."** So the five are a unit: four outer nodes and their
   centre. An outer node is wired only inside its own unit. Units are joined