anchor.diff:  
     @override
     bool operator ==(o) =>
  -      o is Tuple4 && o.i1 == i1 && o.i2 == i2 && o.i3 == i3 && o.i4 == i4;
  +      o is PersistentTuple4 && o.i1 == i1 && o.i2 == i2 && o.i3 == i3 && o.i4 == i4;
   
     @override
     int get hashCode =>
  
positive.code:   String toString() => '[$i1, $i2, $i3, $i4, $i5]';
  
    @override
    bool operator ==(o) => o is Tuple5 &&
        o.i1 == i1 &&
        o.i2 == i2 &&
        o.i3 == i3 &&
  
negative.code:   String toString() => '[$i1, $i2]';
  
    @override
    bool operator ==(o) => o is PersistentTuple2 && o.i1 == i1 && o.i2 == i2;
  
    @override
    int get hashCode => _hash([i1.hashCode, i2.hashCode]);
  