function aff (element)
{
for (i=element; i<=element+3; i++) {
tr = document.getElementById("tr" + i);
tr.style.display = "";
}
}

function cach (element)
{
for (i=element; i<=element+3; i++) {
tr = document.getElementById("tr" + i);
tr.style.display = "none";
}
}