PHP function if function == true

Hello i have problem with the odd or even, i want to do function on that i have this and im getting error: Parse error: syntax error, unexpected 'spocti' (T_STRING), expecting '(' in C:\xampp\htdocs\functions.php on line 34 i have this code

<form method= "post" action= "">
    <input type= "text" name= "cislo" />
    <input type= "submit" name= "submit" />
 </form>

    <?php
        if (isset($_POST['cislo'])){

            $cislo = $_POST['cislo'];

            function spocti(){
                if ($cislo % 2 == 0)
                return true;
            }
        }
        if (function spocti == true){
            echo "Its even";
        }
     ?>