Call to undefined function factorial()

basic_function.php

<?php
/**
 * Created by PhpStorm.
 * User: Mahe
 * Date: 18-May-19
 * Time: 1:11 AM
 */


include_once "functionsss.php";


$x = 5;

echo "Factorial of {$x}  is ".factorial($x);

functionsss.php

<?php
/**
 * Created by PhpStorm.
 * User: Mahe
 * Date: 18-May-19
 * Time: 1:34 AM
 */
function isEven ($myVar){        // Parameters
    if ($myVar%2==0){
        return true;
    }
    return false;
}


function factorialCheck ($myVar){
    $result = 1;
       for ($i= $myVar; $i>1; $i--){

           $result *= $i;
       }
       return $result;
}