'use strict';
  
  var value    = require('../../object/valid-value')
    , aFrom    = require('../from')
    , toArray  = require('../to-array')
    , contains = require('./contains')
    , byLength = require('./_compare-by-length')
  
    , filter = Array.prototype.filter, push = Array.prototype.push;
  
  module.exports = function (/*…lists*/) {
  	var lists, seen, result;
  	if (!arguments.length) return aFrom(this);
  	push.apply(lists = [this], arguments);
  	lists.forEach(value);
  	seen = [];
  	result = [];
  	lists.sort(byLength).forEach(function (list) {
  		result = result.filter(function (item) {
  			return !contains.call(list, item);
  		}).concat(filter.call(list, function (x) {
  			return !contains.call(seen, x);
  		}));
  		push.apply(seen, toArray(list));
  	});
  	return result;
  };