function validate() {
if (document.getElementById("book").name.value == "" ){
  alert("Please enter a name");
  return false;
  }

else if (document.getElementById("book").email.value == "" ) {
  alert("Please enter an email address");
  return false;
  	}
	
else if (document.getElementById("book").tel.value == "" ) {
  alert("Please enter a telephone number");
  return false;
  	}
  
 else {
 return true;
 }
 
}