Review comments

Author: davidben

draft-davidben-tls-merkle-tree-certs.md

@@ -516,11 +516,12 @@ The following procedure can be used to verify a subtree consistency proof.
 
 Given a Merkle Tree over `n` elements, a subtree defined by `[start, end)`, a consistency proof `proof`, a subtree hash `node_hash`, and a root hash `root_hash`:
 
+1. Check that `[start, end)` is a valid subtree ({{definition-of-a-subtree}}), and that `end <= n`. If either do not hold, fail proof verification.
 1. Set `fn` to `start`, `sn` to `end - 1`, and `tn` to `n - 1`.
 1. If `sn` is `tn`, then:
-   1. Right-shift `fn`, `sn`, and `tn` equally until `fn` is `sn`.
+   1. Until `fn` is `sn`, right-shift `fn`, `sn`, and `tn` equally.
 1. Otherwise:
-   1. Right-shift `fn`, `sn`, and `tn` equally until `LSB(sn)` is not set or `fn` is `sn`
+   1. Until `LSB(sn)` is not set or `fn` is `sn`, right-shift `fn`, `sn`, and `tn` equally.
 1. If `fn` is `sn`, set `fr` and `sr` to `node_hash`.
 1. Otherwise:
    1. If `proof` is an empty array, stop and fail verification.