function check_contact_form()
{
 if(document.contact_form.name_f.value == "")  {
   alert("Please type your name");
   document.contact_form.name_f.focus();
   return false;
  }
   else
 if(document.contact_form.email_f.value == "") {
   alert("Please type your e-mail");
   document.contact_form.email_f.focus();
   return false;
  }
  else
 if(document.contact_form.email_f.value.indexOf('@') == -1) {
   alert("E-mail typed not valid");
   document.contact_form.email_f.focus();
   return false;
  }
  else
 if(document.contact_form.comment.value == "") {
   alert("Please type a comment");
   document.contact_form.comment.focus();
   return false;
  }
return true
}