function tab(idlayer) {
var a = idlayer;
if (a=="1") {document.getElementById("tab2").src="images/tab2a.png";
             document.getElementById("tab3").src="images/tab3a.png";
             document.getElementById("tab1").src="images/tab1.png";
             document.getElementById("moreresources").style.visibility="hidden";
             document.getElementById("contact").style.visibility="hidden";
             document.getElementById("welcome").style.visibility="visible";
             document.getElementById("copyright").style.top="400px";
             window.scrollTo(0,0);
             }
else if (a=="2") {document.getElementById("tab1").src="images/tab1a.png";
             document.getElementById("tab3").src="images/tab3a.png";
             document.getElementById("tab2").src="images/tab2.png";
             document.getElementById("welcome").style.visibility="hidden";
             document.getElementById("moreresources").style.visibility="hidden";
             document.getElementById("contact").style.visibility="visible";
             document.getElementById("copyright").style.top="600px";
             window.scrollTo(0,0);
             }
else if (a=="3") {document.getElementById("tab1").src="images/tab1a.png";
             document.getElementById("tab2").src="images/tab2a.png";
             document.getElementById("tab3").src="images/tab3.png";
             document.getElementById("welcome").style.visibility="hidden";
             document.getElementById("contact").style.visibility="hidden";
             document.getElementById("moreresources").style.visibility="visible";
             document.getElementById("copyright").style.top="2200px";
             window.scrollTo(0,0);
             }     
}