var hideable_elements = new Array()
    
function toggleElementVisible(element_id) {
    if (hideable_elements[element_id] != 1) {
        hideable_elements[element_id] = 1
        document.getElementById(element_id).style.display = ""
    }
    else {
        hideable_elements[element_id] = 0
        document.getElementById(element_id).style.display = "none"
    }   
}