anchor.diff:    };
   
     const $tabs = $('.tab-filenames');
  +  const $selectedTab = () => $('.selected', $tabs);
  +  const currentFilename = () => $filenameTab().text();
     const alreadySelected = $tab => $tab.hasClass('selected');
     const select = $tab => {
       $('.tab-filename').removeClass('selected');
       $tab.addClass('selected');
     };
  -  const selectedTabFilename = () => $('.selected', $tabs).text();
  -
  -  const currentFilename = () => $filenameTab().text();
   
     cd.isOutputFile = filename => ['stdout','stderr','status',$replTab().text()].includes(filename);
   
  
positive.code: 
    cd.setFilenameTab = (filename) => {
      // filename = from filename-knave, stdout, stderr, status (never +REPL)
      if (selectedTabFilename() === $replTab().text()) {
        cd.closeRepl();
      }
      const id = cd.isOutputFile(filename) ? `radio_${filename}` : 'current_filename';
  
negative.code:   // Alt-O ==> toggleOutputFile()
  
    cd.toggleOutputFile = () => {
      switch ($selectedTab().text()) {
      default               : cd.loadFile('stdout'); break;
      case 'stdout'         : cd.loadFile('stderr'); break;
      case 'stderr'         : cd.loadFile('status'); break;
  