diff --git a/CHANGELOG.md b/CHANGELOG.md
index 09d97f2..a630eb8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -32,8 +32,10 @@ and answers with the error page. It used to leave some grants gone and the membe
 
 ### The admin example removes a deleted group from the groups it was nested in
 
-Deleting a group now also deletes the tuples that made it a member of another group, in the same
-transaction. It used to leave them, so a group re-created with the same name was back in every parent.
+Deleting a group now also removes it from every group it was a member of, in the same Keto
+transaction as the rest. It used to stay listed there, so a group re-created with the same name was
+back in every parent. A parent whose only member was the deleted group is left with no members, and
+so no longer exists as a group.
 
 ### The admin example keeps a user's permissions section when it refuses a self-deactivate or self-delete
 
diff --git a/examples/plugins/auth-admin/admin-groups.ts b/examples/plugins/auth-admin/admin-groups.ts
index 3ef5d4d..4b869fc 100644
--- a/examples/plugins/auth-admin/admin-groups.ts
+++ b/examples/plugins/auth-admin/admin-groups.ts
@@ -2,7 +2,7 @@
 // A group is a Keto subject set `Group:<name>#members`; a member is a user or a nested group (see
 // parseSubject). Writes go only to Keto (README "stateless"). Keto has no "create object" — a group
 // exists exactly while it has ≥1 member, so create writes its first-member tuple and delete removes
-// every member tuple. Pure builders turn tuples + the request URL into view models; below them are thin
+// every tuple that makes it a group or puts it in another. Pure builders turn tuples + the request URL into view models; below them are thin
 // per-route handlers (keyed on ctx.params) over a shared `withGroups` gate — admin-only, CSRF-guarded,
 // each returning a RouteResult.
 
@@ -428,8 +428,10 @@ export const groupsDelete = withGroupName(async (deps, name) => {
   const lost = await lostOnDelete(deps, name);
   if (lost.length > 0) return refuseSelfLockout(deps, name, "delete", lost);
   // A Keto set exists only through its tuples, so leaving the grants or the parents' membership
-  // tuples behind would resurrect every permission and nesting the moment someone re-created a
-  // group with the same name.
+  // tuples behind would resurrect every permission and parent membership the moment someone
+  // re-created a group with the same name. A parent that had only this group as a member is left
+  // with none and so ceases to exist, as when its last member is removed by hand; its own grants
+  // and parent memberships stay (todo.md).
   const subject = groupSubject(name);
   const held = await heldPermissions(keto, subject);
   const grants = held.map((permission) => grantTuple(permission, subject));
diff --git a/todo.md b/todo.md
index 8ea3a4b..848f488 100644
--- a/todo.md
+++ b/todo.md
@@ -6,7 +6,7 @@
 
 `Bar = 1`
 
-`Next ID = 72`
+`Next ID = 73`
 
 ## Items
 
@@ -15,6 +15,7 @@
 | 19 | 0.6.0 |  | question | **Run the documented Docker commands on macOS and fix whatever misbehaves.** | 2 | 2 | 1 | 3 | 3 | 1 by 3 | 3.3 |
 | 16 | 0.6.0 |  | question | **Decide whether the single Keto `Resource` namespace splits into per-domain namespaces.** | 3 | 2 | 3 | 6 | 6 | 7 by 2 | 0.5 |
 | 65 | 0.6.0 |  |  | **Export `KetoError` from `@plainpages/plugin-api`, so a plugin can tell a Keto failure apart with `instanceof`.** | 1 | 2 | 1 | 2 | 1 | 7 by 3, 1 by 1 | 6.7 |
+| 72 | 0.6.0 |  |  | **Delete a group's grants and parent memberships when its last member leaves, by group delete or by removing the member, so re-creating the name restores none.** | 2 | 2 | 2 | 4 | 3 | 2 by 4 | 4.2 |
 | 67 | 0.6.0 |  |  | **Group `src/auth`'s modules into one subfolder per concern, with `bootstrap.ts` staying at `src/auth/bootstrap.ts`.** | 3 | 1 | 2 | 4 | 6 | code health by 4 | 4.0 |
 | 14 | 0.6.0 |  |  | **Drop a double-clicked duplicate submit, with no client-side JavaScript.** | 4 | 2 | 3 | 7 | 7 | 2 by 7, 1 by 4 | 1.4 |
 
@@ -43,6 +44,28 @@ surface, so this adds to the plugin API: it ships in a minor, and `HOST_API_VERS
 `0.6.0` when 0.6.0 is tagged (AGENTS.md → Rules). Adding is safe for installed plugins; removing it
 later would take a major.
 
+### 72. Delete a group's grants and parent memberships when its last member leaves, by group delete or by removing the member, so re-creating the name restores none.
+
+In `examples/plugins/auth-admin/admin-groups.ts` a group exists exactly while it has a
+`Group:<name>#members` tuple. Two paths empty a group but keep its other tuples, so re-creating the
+name silently hands every new member the old permissions and parent memberships:
+
+1. `groupsDelete` of a group that is a parent's only member: the parent ceases to exist but keeps
+   its `Permission:*#granted@Group:<parent>#members` grants and its memberships in grandparents.
+2. `groupsRemoveMember` removing a group's last member, which today is a lone `deleteTuple`.
+
+Fix both in one `transactTuples` with the removal: when the removal leaves a group with no members,
+add its grants and the tuples naming it as a member of other groups to the delete. The cascade is
+transitive: a grandparent emptied by its parent vanishing is the same bug one level up. The walk
+stops at a group that keeps any member, so a nesting cycle (`groupsAddMember` refuses only a
+self-nest) ends it. An emptied group grants nobody, so the cascade cannot change what
+`lostToSelf` computes. Test it with nesting two levels deep and with a cycle.
+
+When it ships, rewrite the comment at `groupsDelete` that points here, and the CHANGELOG entry "The
+admin example removes a deleted group from the groups it was nested in", which then says a parent
+left with no members no longer exists as a group. `lostToSelf`, in this file, is a place the seats
+found hard; if the change touches it, make it easier to read.
+
 ### 67. Group `src/auth`'s modules into one subfolder per concern, with `bootstrap.ts` staying at `src/auth/bootstrap.ts`.
 
 `src/auth` holds 19 modules over several concerns: the per-request session path (`jwt*`, `jwks`,