<?
 
$links = '
			<a href="?action">action</a>: </br>
			<a href="?action=page1">action=page1</a>: </br>
			<a href="?action=page2">action=page2</a>:</br>
			<a href="?action=page3">action=page3</a>:</br>
			<a href="?action=page4">action=page4</a>:</br>
			</br>
			<a href="?action1">action1</a>: </br>
			<a href="?action1=page1">action1=page1</a>: </br>
			<a href="?action1=page2">action1=page2</a>:</br>
			<a href="?action1=page3">action1=page3</a>:</br>
			<a href="?action1=page4">action1=page4</a>:</br>
		';
		
if (isset($_GET['action'])) {  

	if ($_GET['action'] == "") 
	{ 
		echo 
		"
			первая страница action </br></br>
			$links
		"; 
	} 

	else if ($_GET['action'] == "page1") 
	{ 
		echo 
		"
			action=page1 </br></br>
			$links
		";
	} 
	else if ($_GET['action'] == "page2") 
	{ 
		echo 
		"
			action=page2 </br></br>
			$links	
		";
	}

	else if ($_GET['action'] == "page3") 
	{ 
		echo 
		"
			action=page3 </br></br>
			$links
		";
	}
	else 
	{ 
		echo 
		"
			такой страницы нет !!! </br></br>
			$links
		";
	}
}

elseif(isset($_GET['action1'])) {  

	if ($_GET['action1'] == "") 
	{ 
		echo 
		"
			первая страница action1 </br></br>
			$links
		";
	} 

	else if ($_GET['action1'] == "page1") 
	{ 
		echo 
		"
			action1=page1 </br></br>
			$links
		";
	} 
	else if ($_GET['action1'] == "page2") 
	{ 
		echo 
		"
			action1=page2 </br></br>
			$links
		";
	}

	else if ($_GET['action1'] == "page3") 
	{ 
		echo 
		"
			action1=page3 </br></br>
			$links
		";
	}
	else 
	{ 
		echo 
		"
			такой страницы нет !!! </br></br>
			$links
		";
	}
}


?>