What are you trying to perform here? define constructs a constant, and it should not be used as a comparator. Ie:
Would result in:
define('A', 'a value');
What you are doing cannot be used in a constant as the characters are invalid (they must follow variable naming conventions).
<b>Warning</b>: define() expects at least 2 parameters, 1 given in <b>[...][...]</b> on line <b>3</b><br />
Something brokea value
You'll need to use some type of persisting data in order to determine if you should go somewhere. Perhaps you are intending to use something like file_exists?