$element) {
		if (trim($element["ID"]) === $value) {
			return $element["ID"];
		}
	}
}

$arr = array(

);

$arr1 = array (
	"0" => array(
		"art" => "546436456",
	),	
	"1" => array(
		"art" => "7683435",
	),
);

$arr2 = array (
	"0" => array(
		"art" => "546436456",
	),	
	"1" => array(
		"art" => "76653834543283435",
	),
);

$arr3 = array (
	"0" => array(
		"art" => "546436456",
	),	
	"1" => array(
		"art" => "45435233",
	),
);

echo "Arr1 | 
";
foreach ($arr1 as $i => $el) {
	if (empty(searchElementArr($el["art"], $arr))) {
		array_push($arr, array(
			"ID" => $el["art"],
		));
		echo "
 Товар добавлен [art] => ".$el["art"]." 
";
	} else { echo "
 Товар изменён 
"; }
}

echo "
 Arr2 | 
";
foreach ($arr2 as $i => $el) {
	if (empty(searchElementArr($el["art"], $arr))) {
		array_push($arr, array(
			"ID" => $el["art"],
		));
		echo "
 Товар добавлен [art] => ".$el["art"]." 
";
	} else { echo "
 Товар изменён [art] => ".$el["art"]." 
"; }
}

echo "
 Arr3 | 
";
foreach ($arr3 as $i => $el) {
	if (empty(searchElementArr($el["art"], $arr))) {
		array_push($arr, array(
			"ID" => $el["art"],
		));
		echo "
 Товар добавлен [art] => ".$el["art"]." 
";
	} else { echo "
 Товар изменён [art] => ".$el["art"]." 
"; }
}

echo "
 Итоговый масив Arr | 
";
print_r($arr);

?>