var is_open = 0;
var has_text = [false, false, true, true, true, true];

function open_close(n) {
    var was_open = (n == is_open);
    var will_show_text = (has_text[n-1] && !was_open); // must have text and needs to have been closed before
    var base_opacity = will_show_text ? 0.3 : 1;

    // hide all
    for(var i=0; i<is_open.length; ++i) {
        document.getElementById('text'+(i+1)).style.visibility = 'hidden';
        document.getElementById(i+1).style.opacity = base_opacity;
        is_open[i] = false;
    }

    if (will_show_text) {
        document.getElementById('text'+n)).style.visibility = 'visible';
        document.getElementById(n).style.opacity = '1';
        is_open[n-1] = true;
    }
}

function myFunction() { open_close(1); }
function myFunction2() { open_close(2); }
function myFunction3() { open_close(3); }
function myFunction4() { open_close(4); }
function myFunction5() { open_close(5); }
function myFunction6() { open_close(6); }