function vth(d,i){
	if (d == "next") {
		document.getElementById(("v"+i+"t" + c[i])).style.visibility = 'hidden';
		document.getElementById(("v"+i+"t" + n[i])).style.visibility = "visible";
		++p[i];
		++c[i];
		++n[i];
		vtl(d,i);
	}
	if (d == "prev") {
		document.getElementById("v"+i+"t" + c[i]).style.visibility = 'hidden';
		document.getElementById("v"+i+"t" + p[i]).style.visibility = "visible";
		--p[i];
		--c[i];
		--n[i];
		vtl(d,i);
	}
}

function vtl(e,i){
	if (e == "next") { 
		if (p[i] > vtmax[i])
			p[i] = 1;
		if (c[i] > vtmax[i])
			c[i] = 1;
		if (n[i] > vtmax[i])
			n[i] = 1;
	}
	if (e == "prev") {
		if (p[i] < 1)
			p[i] = vtmax[i];
		if (c[i] < 1)
			c[i] = vtmax[i];
		if (n[i] < 1)
			n[i] = vtmax[i];
	}
}