Warning: Undefined array key "teRaden" in own project

Question

Sorry, but i just don't see it. Can anybody help? The warning that is given warns that I didn't define a array key. But if I do define it in the start of the code, from'if(isset($COOKIE).. etc., I get curly rounds under my code, so that's not the answer. I'm lost here.

What should I do? Alsof, if I do the guessing in my browser it just says 'target lower'. I know i have to set a generated number, but where?

<?php
session_start();

$i_laagste = '1';
$i_hoogste = '10'; 

if(isset($_COOKIE['aanHetSpelen']) && $_COOKIE['aanHetSpelen'] == "ja" ) :
    $i_teRaden = $_SESSION["teRaden"] ;
else :
    $i_teRaden = random_int($i_laagste, $i_hoogste) ; // i = integer
    setcookie("aanHetSpelen","ja", time()+60*60*24*30) ; // 30 dagen
    $_SESSION["teRaden"] = $i_teRaden ;
    $_SESSION["pogingen"] = array() ;
endif ;
$s_welkom = "Welkom bij dit spel" ;
$s_hoger = "U moet hoger raden" ;
$s_lager = "U moet lager raden" ;
$s_goed = "U heeft goed geraden" ;
$html_form_start = '<form action="" method="get">' ;
$html_form_end = '</form>' ;
$html_form_content = '' ; // lege string, zou ook null mogen zijn
for($teller = $i_laagste ; $teller <= $i_hoogste ; $teller++){
    $html_form_content .= '<input type="submit" value="'.$teller.'" name="getal">' ;
}
 
/* motor is included, the content of the motor is 

<?php
function motor($i_teRaden, $s_lager, $s_hoger, $s_goed, $s_welkom) {
    // na de variabelen komt de motor (het programma)
    if(array_key_exists('getal',$_GET) && is_numeric($_GET['getal'])){
        // tel de beurt erbij
        $_SESSION["pogingen"][] = $_GET['getal'] ;
        if ($_GET["getal"]>$i_teRaden) {
            $s_output = $s_lager ;
        } elseif ($_GET["getal"]<$i_teRaden) {
            $s_output = $s_hoger ;
        } elseif ($_GET["getal"]==$i_teRaden) { // vergelijking hoeft eigenlijk niet
            $s_output = $s_goed ;
            // schrijf naar het bestand
            // fopen, fwrite, fclose
            $r_bestand = fopen('spelletje.log', 'a') ;
            $content = json_encode($_SESSION) . PHP_EOL;
            fwrite($r_bestand, $content) ;
            fclose($r_bestand) ;
            // zet het spel in de nieuwe startstand
            setcookie("aanHetSpelen","nee", time()-60*60*24*30) ;
            session_destroy() ;
        }
    } else {
        $s_output = $s_welkom ;
    }
    return $s_output ;
}

*/


include 'motor.php' ;
$s_output = motor($i_teRaden, $s_lager, $s_hoger, $s_goed, $s_welkom) ;




$html_form_output = $html_form_start . $html_form_content . $html_form_end ;

?>