to return value in function php from XML files

I need help doing this. i cant figure out how to retu the boolean, and it seems that my condition's not working.

<?php


$xml=simplexml_load_file("Details.xml") or die("Error: Caot create object");


function SearchSu($Su1 , $Su2)
{
    //boolean 
    $av1 = false; //false => the supervisor is not in the list (AVAILABLE)
    $av2 = false;

    //set the  supervisor
    $Su1 = "591006125411"; //Bruno
    $Su2 = "571121125351"; //Dayana

    foreach($xml_array as $Employee) //problem occur here though
    {
        if($Su1 == $Employee->EmployeeNewIC) // true=>supervisor is out
        {
            //if supervisor1 is out, procees check with supervisor2
            if($Su2 == $Employee->EmployeeNewIC ) 
            {   
                retu $av1 = false; //true=>supervisor is out 

            }
            else if($Su2 !== $Employee->EmployeeNewIC) // false=>supervisor is available
            { 
                retu $av2;    
            }
        }
        else
            retu $av1;

    }
SearchSu("591006125411","571121125351");

?>

i would very much appreciate the help.