public static function fileExistsCS($sFilename)
    {
        if (array_key_exists($sFilename, static::$aFileExistsCache)) {
            return static::$aFileExistsCache[$sFilename];
        }

        $sDirectory = dirname($sFilename);
        $aFiles     = array_map(function ($sFile) {
            return basename($sFile);
        }, glob($sDirectory . DIRECTORY_SEPARATOR . '*', GLOB_NOSORT));

        if (in_array(basename($sFilename), $aFiles)) {
            //  Test if the directory exists
            $bResult = static::isDirCS($sDirectory);
        } else {
            $bResult = false;
        }

        static::$aFileExistsCache[$sFilename] = $bResult;
        return $bResult;
    }