diff --git a/03-DESIGN/01-to-be/47-milestones/G-20-lead-answers.md b/03-DESIGN/01-to-be/47-milestones/G-20-lead-answers.md
index db84c24c..c7555817 100644
--- a/03-DESIGN/01-to-be/47-milestones/G-20-lead-answers.md
+++ b/03-DESIGN/01-to-be/47-milestones/G-20-lead-answers.md
@@ -347,3 +347,7 @@ names the principle that settles it, and is cited as "design 47 G A-n".
 - **A-89** (§37, §700, A-74; principle 7, one way for every asker) The runner reads its approval ask's warrant from the
   router's record of its ask, through the seat `operator-channel` as A-74 has it, never from the decided event's body;
   the decided event only wakes it.
+- **A-90** (§13, §14, §291, ADR 0666 §6, A-85; principle 7) A non-first branch's revision is made by the same take-in as
+  the trunk's, taken per watched branch: `sourceFollow` takes `source.<branch>` for every watched branch, and the
+  source path (`ApplySource`, the catch-up, the heads' take-in) runs with the branch as its argument, writing that
+  branch's revision; the trunk is each registration's first branch, not a constant.