covered neighbours have it

1 files changed, 8 insertions, 0 deletions

diff --git a/docs/peers.md b/docs/peers.md
index 70437ab..4ee3c16 100644
--- a/docs/peers.md
+++ b/docs/peers.md
@@ -355,6 +355,14 @@ reaches no other member, by its parent's), or can't apply the next message and a
 what it lacks, and gets just that, and what that builds on, again (not what was sent
 after it: that may only be late).
 
+A node's neighbours that get a writer's changes from another parent in its tree, and
+the writer, count as having them: what it passes on to them later along other trees
+doesn't carry them again. Without that, with writers in turn, each change coming along
+another tree, the node's view of a neighbour stays as of its last message to it, and
+the next carries all it got since, nearly all of it brought by the neighbour's other
+parents (with 50 nodes and writers in turn, about ten changes per message, one of them
+new). Should one lack them after all, it asks, as above.
+
 As nobody waits for these answers, messages overtake each other on slow links. Three
 things keep that from sending changes twice (`document::sync`):