function callNavi(imgName, bVisible) {
  var anchor = document.getElementById(imgName);
  anchor.style.visibility = bVisible? "visible": "hidden";
}

function pressKey(e) {
  var keycode = (e == null)? event.keyCode: e.which; // ie : mozilla
  var key = String.fromCharCode(keycode).toLowerCase(); // to lowercase

  if (key == "v") {
    var oHref = document.getElementById('hrefP');
    if (oHref!=null) document.location.href = document.getElementById('hrefP');
  }  else if (key == "n") {
    var oHref = document.getElementById('hrefN');
    if (oHref!=null) document.location.href = document.getElementById('hrefN');
  }
}

document.onkeypress = pressKey;