Term.prototype.setUnion = function(other) {
  if (this._fastArity(arguments.length, 1) === false) {
    var _len = arguments.length; var _args = new Array(_len);
    for (var _i = 0; _i < _len; _i++) {_args[_i] = arguments[_i];}
    this._arity(_args, 1, 'setUnion', this);