+;;
+
+let usage_string =
+"
+<html>
+ <head>
+ <title>ProofChecker's help message</title>
+ </head>
+ <body>
+ <h1>ProofChecker</h1>
+ <h2>Usage</h2>
+ <p>
+ Usage: <kbd>http://hostname:proofcheckerport/</kbd><em>command</em>
+ </p>
+ <p>
+ Available commands:
+ </p>
+ <p>
+ <b><kbd>help</kbd></b><br />
+ display this help message
+ </p>
+ <p>
+ <b><kbd>proofCheck?uri=uri</kbd></b><br />
+ proof-checks the object whose URI is specified by <em>uri</em>
+ </p>
+ </body>
+</html>
+"
+;;
+
+let outchan = ref stderr;;