diff --git a/ForumApp.markdown b/ForumApp.markdown
index 56b03d1..32f8b39 100644
--- a/ForumApp.markdown
+++ b/ForumApp.markdown
@@ -1,4 +1,4 @@
-ForumApp is a [BSP application](BSP) that synchronises forum posts among groups of devices. Devices join forums by invitation.
+ForumApp is a [BSP application](BSP) that synchronises forum posts among groups of devices.
 
 ### Channel identifiers
 
@@ -29,8 +29,8 @@ The application identifer is random:
 * An invitation or response must belong to the invitation channel.
 * A post or attachment must belong to a forum channel.
 * An invitation is valid if it is well-formed.
-* A response is valid if it is well-formed and references a valid invitation created by the opposite device.
-* A departure is valid if it is well-formed and references a valid invitation created by either device.
+* A response is valid if it is well-formed and it references a valid invitation created by the opposite device.
+* A departure is valid if it is well-formed and it references a valid invitation created by either device.
 * A post is valid if it is well-formed, its parent (if any) is a valid post, and it is either anonymous or carries a valid signature over its content.
 * An attachment is always valid.