diff --git a/src/Pure/Tools/flarum.scala b/src/Pure/Tools/flarum.scala
--- a/src/Pure/Tools/flarum.scala
+++ b/src/Pure/Tools/flarum.scala
@@ -1,32 +1,32 @@
 /*  Title:      Pure/General/flarum.scala
     Author:     Makarius
 
 Support for Flarum forum server: https://flarum.org
 */
 
 package isabelle
 
 
 import java.net.URL
 
 
 object Flarum
 {
   // see RFC3339 in https://www.php.net/manual/en/class.datetimeinterface.php
-  val Date_Format = Date.Format("uuuu-MM-dd'T'HH:mm:ssxxx")
+  val Date_Format: Date.Format = Date.Format("uuuu-MM-dd'T'HH:mm:ssxxx")
 
   def server(url: URL): Server = new Server(url)
 
   class Server private[Flarum](url: URL)
   {
     override def toString: String = url.toString
 
     def get(route: String): HTTP.Content =
       HTTP.Client.get(if (route.isEmpty) url else new URL(url, route))
 
     def get_api(route: String = ""): JSON_API.Root =
       JSON_API.Root(get("api" + (if (route.isEmpty) "" else "/" + route)).json)
 
-    val api: JSON_API.Root = get_api()
+    val root: JSON_API.Root = get_api()
   }
 }