nl_tokens: private _uniqContentEquals function . That function is checking equality of 2 iterator contents with 2 assumptions - iterators lengths are the same - iterators values are unique
pl_tokens: function _uniqContentEquals ( aIterator , bIterator , stackA , stackB ) { var a = _arrayFromIterator ( aIterator ) ; var b = _arrayFromIterator ( bIterator ) ; function <mask> ( _a , _b ) { return _equals ( _a , _b , stackA . slice ( ) , stackB . slice ( ) ) ; } // if *a* array contains any element that is not included in *b* return ! _containsWith ( function ( b , aItem ) { return ! _containsWith ( eq , aItem , b ) ; } , b , a ) ; }