function a() { document.nav1.src="main_page_in.gif";}
function b() { document.nav1.src="main_page_out.gif";} 
function c() { document.nav2.src="thumbnails_in.gif";}
function d() { document.nav2.src="thumbnails_out.gif";}
function e() { document.nav3.src="prior_pic_in.gif";}
function f() { document.nav3.src="prior_pic_out.gif";} 
function g() { document.nav4.src="next_pic_in.gif";}
function h() { document.nav4.src="next_pic_out.gif";}
function i() { document.nav5.src="main_page_in.gif";}
function j() { document.nav5.src="main_page_out.gif";} 
function k() { document.nav6.src="thumbnails_in.gif";}
function l() { document.nav6.src="thumbnails_out.gif";} 
function m() { document.nav7.src="prior_pic_in.gif";}
function n() { document.nav7.src="prior_pic_out.gif";}
function o() { document.nav8.src="next_pic_in.gif";}
function p() { document.nav8.src="next_pic_out.gif";}