diff --git a/go/buscompose/names_test.go b/go/buscompose/names_test.go
index da93c34..2f0b5cc 100644
--- a/go/buscompose/names_test.go
+++ b/go/buscompose/names_test.go
@@ -18,6 +18,12 @@ func TestTheBusNamesAgree(t *testing.T) {
 	if LogStreamName("mesh-delivery-builder", "build-log") == "" || LogSubject("mesh-delivery-builder", "build-log") == "" {
 		t.Fatal("a log has no stream or subject")
 	}
+	// 1966/AC20: a ledger's history and snapshot subjects are one contract, which the grants part grants a ledger
+	// account its publish on.
+	if h, sn := LedgerHistorySubject("m", "records"), LedgerSnapshotSubject("m", "records"); h != "mesh.ledger.m.records.history" ||
+		sn != "mesh.ledger.m.records.snapshot" {
+		t.Fatalf("a ledger's subjects are %q and %q", h, sn)
+	}
 	// 1966/AC23: a wanted account of kind ledger for m on a names the user ledger.a.m and the own secret ledgers.
 	ledger := WantedAccount{User: "ledger.a.m", Kind: KindLedger, Node: "a", Module: "m", URL: "nats://10.0.0.1:4222"}
 	if got := (Principal{Kind: KindLedger, Node: "a", Module: "m"}).Username(); got != "ledger.a.m" {
diff --git a/go/buscompose/nats.go b/go/buscompose/nats.go
index c0f2618..f7f8ba8 100644
--- a/go/buscompose/nats.go
+++ b/go/buscompose/nats.go
@@ -50,6 +50,20 @@ const (
 	KindLedger Kind = "ledger"
 )
 
+// LedgerHistorySubject and LedgerSnapshotSubject are the subject prefixes of one ledger's history and of its instances'
+// snapshots (novox/hq ADR 0597 §1, §8, §9): an instance's subject is the prefix, ".", and the instance's path with each
+// "/" written "." (`decision/0290` is `….decision.0290`). One contract: the grants part grants a ledger account its
+// publish on them, the tool runner appends and snapshots on them, and the bus module creates the history's stream over
+// them.
+func LedgerHistorySubject(module, local string) string {
+	return "mesh.ledger." + module + "." + local + ".history"
+}
+
+// LedgerSnapshotSubject is the subject prefix of one ledger's instances' snapshots (LedgerHistorySubject).
+func LedgerSnapshotSubject(module, local string) string {
+	return "mesh.ledger." + module + "." + local + ".snapshot"
+}
+
 // Seat is a role on the bus as a principal relates to it: the subjects it accepts, and those it
 // emits (novox/hq ADR 0118, design 29 §5).
 type Seat struct {