https://www.mongodb.com/docs/manual/core/document/
https://www.mongodb.com/docs/manual/reference/operator/query/
https://www.mongodb.com/docs/manual/reference/operator/update/
https://www.mongodb.com/docs/manual/reference/operator/aggregation-pipeline/
https://www.mongodb.com/docs/manual/reference/operator/aggregation/

$lt
..
$add
$multiply