<?php if !($name == "" || $email == "" || $quest == ""){ <form action="quest_action.php" method="post"></form> } ?>
_____ _ _ А + В = А * В
if ($name != "" && $email != "" && $quest != ""){ echo '<form action="quest_action.php" method="post"></form>'; }
($name == "" || $email == "" || $quest == ")
if (!strlen($name)) ... if (empty($name)) ...
if if (!($name == "" || $email == "" || $quest == "")) { echo '<form action="quest_action.php" method="post"></form>'; }