Redefine Funtion

Dear List - Thanks for all your help with my previous question. This works -

      $output = shell_exec('php P7a.php');
      echo $output;

Now another question -

    function SetParameters()
    {
     etc......
    }

switch ($_POST['next_step']) { case 'step1': { SetParameters(); Choice(); break; }

        } //end switch

// yes, there are more cases, and I have checked for mismatched parenthesis and have not found //any. Fatal error: Cannot redeclare SetParameters() (previously declared in /var/www/P7a.php:109) in /var/www/P7a.php on line 180 ??? TIA Ethan