diff --git a/src/Pure/Admin/build_easychair.scala b/src/Pure/Admin/build_easychair.scala
--- a/src/Pure/Admin/build_easychair.scala
+++ b/src/Pure/Admin/build_easychair.scala
@@ -1,108 +1,108 @@
 /*  Title:      Pure/Admin/build_easychair.scala
     Author:     Makarius
 
 Build Isabelle component for Easychair style.
 
-See also: https://easychair.org/publications/for_authors
+See also https://easychair.org/publications/for_authors
 */
 
 package isabelle
 
 
 object Build_Easychair {
   /* build easychair component */
 
   val default_url = "https://easychair.org/publications/easychair.zip"
 
   def build_easychair(
     download_url: String = default_url,
     target_dir: Path = Path.current,
     progress: Progress = new Progress
   ): Unit = {
     Isabelle_System.require_command("unzip", test = "-h")
 
     Isabelle_System.with_tmp_file("download", ext = "zip") { download_file =>
       Isabelle_System.with_tmp_dir("download") { download_dir =>
 
         /* download */
 
         Isabelle_System.download_file(download_url, download_file, progress = progress)
         Isabelle_System.bash("unzip -x " + File.bash_path(download_file),
           cwd = download_dir.file).check
 
         val easychair_dir =
           File.read_dir(download_dir) match {
             case List(name) => download_dir + Path.explode(name)
             case bad =>
               error("Expected exactly one directory entry in " + download_file +
                 bad.mkString("\n", "\n  ", ""))
           }
 
 
         /* component */
 
         val version =
           Library.try_unprefix("EasyChair", easychair_dir.file_name)
             .getOrElse("Failed to detect version from " + quote(easychair_dir.file_name))
 
         val component = "easychair-" + version
         val component_dir = Isabelle_System.new_directory(target_dir + Path.basic(component))
         progress.echo("Component " + component_dir)
 
         component_dir.file.delete
         Isabelle_System.copy_dir(easychair_dir, component_dir)
 
 
         /* settings */
 
         val etc_dir = Isabelle_System.make_directory(component_dir + Path.basic("etc"))
         File.write(etc_dir + Path.basic("settings"),
           """# -*- shell-script -*- :mode=shellscript:
 
 ISABELLE_EASYCHAIR_HOME="$COMPONENT"
 """)
 
 
         /* README */
 
         File.write(component_dir + Path.basic("README"),
           """This is the Easychair style for authors from
 """ + download_url + """
 
 
     Makarius
     """ + Date.Format.date(Date.now()) + "\n")
       }
     }
   }
 
 
   /* Isabelle tool wrapper */
 
   val isabelle_tool =
     Isabelle_Tool("build_easychair", "build component for Easychair style",
       Scala_Project.here,
       { args =>
         var target_dir = Path.current
         var download_url = default_url
 
         val getopts = Getopts("""
 Usage: isabelle build_easychair [OPTIONS]
 
   Options are:
     -D DIR       target directory (default ".")
     -U URL       download URL (default: """" + default_url + """")
 
   Build component for Easychair style.
 """,
           "D:" -> (arg => target_dir = Path.explode(arg)),
           "U:" -> (arg => download_url = arg))
 
         val more_args = getopts(args)
         if (more_args.nonEmpty) getopts.usage()
 
         val progress = new Console_Progress()
 
         build_easychair(download_url = download_url, target_dir = target_dir, progress = progress)
       })
 }