function setDisplay(objectID,state) {
    var object = document.getElementById(objectID);
    object.style.display = state;
}
function show (id) {
    setDisplay('plus'+id, 'none')
    setDisplay('minus'+id, 'block')
}
function hide (id) {
    setDisplay('minus'+id, 'none')
    setDisplay('plus'+id, 'block')
}