``` javascript
db.foo.insertOne({"jabłko" : 1, "banan" : 6, "gruszka" : 3})
db.foo.insertOne({"jabłko" : 8, "szpinak" : 4, "melon" : 4})
db.foo.find({"$where" : function () { 
	for (var current in this) { 
		for (var other in this) {
			if (current != other && this[current] == this[other]) 
				{ return true; } 
		}
	}
	return false;
}});
```