$navigation_map = {
	first_page       => {
		PREVIOUS => '',
		NEXT     => 'second_page',
	},
	second_page      => {
		PREVIOUS => 'first_page',
		NEXT     => 'third_page',
	},
 	third_page         => {
		PREVIOUS => 'second_page',
		NEXT     => 'fourth_page',
	},
	fourth_page         => {
		PREVIOUS => 'third_page',
		NEXT     => '',
	},
};