dist/util.js
function seen(o1, o2) {
  var i, len;

  for (i = 0, len = seenObjects.length; i < len; i++) {
    if (seenObjects[i][0] === o1 && seenObjects[i][1] === o2) {
      return true;
    }
  }

  return false;
}
function seen(o1, o2) {
  var i, len;

  for (i = 0, len = seenObjects.length; i < len; i++) {
    if (seenObjects[i][0] === o1 && seenObjects[i][1] === o2) {
      return true;
    }
  }

  return false;
}
Internal: Used by `detectRecursion` to check to see if the given pair of objects has been encountered yet on a previous recursive call.  o1 - The first object to check for recursion. o2 - The paired object to check for recursion.  Returns `true` if the pair has been seen previously and `false` otherwise.