php syntax error on line 9

I have been staring at this for an hour now. It says I
have an

Parse error: syntax error, unexpected '{' in line 9.

Could someone please look at this for me.
Thanks in
advance.

if(isset($_POST['submit']))
{

            function foo($a, $b)
{

 foreach(array_keys($a) as
            $i)
 {
 if(array_key_exists($i, $b){
 $result[$i] =
            $a[$i]*$b[$i];
 }else{
 $result[$i] = 0;
 }

            }
 foreach(array_keys($b) as $i)
 {

 if(not
            array_key_exists($i, $a){ //exists in b but not i a
 $result[$i] =
            0;
 }
 }
 return
            $result
}
}

?>