function array_display($array, $pre=FALSE){
$tag = $pre ? 'pre' : 'p';
printf("<%s>%s\n", $tag, var_export($array, TRUE), $tag);
}
$arr1 = array(1, 2, 3);
$arr2 = array(10, 20, 30);
$arr3 = array(5, 10, 15, 20);
$comb1 = array_merge($arr1, $arr2);
$comb2 = array_merge($arr2, $arr1);
$comb3 = array_merge($arr3, $arr2, $arr1);
array_display($comb1);
array_display($comb2);
array_display($comb3);
?>
$arr4 = array(10 => 'a', 11 => 'b', 12 => 'c');
array_display(array_merge($arr1, $arr4), TRUE);
array_display($arr1 + $arr4, TRUE);
?>
$arr5 = array(1 => 'x', 2 => 'y', 3 => 'z');
array_display(array_merge($arr1, $arr5), TRUE);
array_display($arr1 + $arr5, TRUE);
?>
$dogs1 = array( 'L' => 'C', 'B' => 'S','R' => 'A');
$dogs2 = array('R' => 'D', 'T' => 'S');
array_display(array_merge($dogs1, $dogs2), TRUE);
array_display($dogs1 + $dogs2, TRUE);
?>