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17If "at the expense of" is used it is necessary to provide or explain that certain enrichments which might be thought to be at the expense of another in ordinary language are not so regarded for the purposes of this branch of the law.
18This is made clear in the draft rules under consideration by the Study Group.
19See the second edition of this book at p 386.
20A person who has, in error, transferred property which has no value or which is actually burdensome to the recipient can still require its return. It might, after all, be of some value or use to the transferor even if not to the transferee.
21One classic case is where something has passed from each party to the other under a void contract. Of course, even on the "economic" approach, this problem can be solved by a specific provision.