function check_categ(myform){
  for (i = 0; i < myform.categ.length; i++){ 
    if(myform.categ[i].checked){
      return myform.categ[i].value
    } 
  } 
}

function on_t_field_enter(myform,call_back){
  if(window.event && window.event.keyCode == 13){
    return call_back(myform);
  }else{
    return true;
  }
}

var ama_search_callback = function(myform){
  return location.href='http://amazon.yokocyo.com/search/'+myform.nt.value+'/'+check_categ(myform)+'_'+myform.keyword.value+'_1.html';
}